High temperature energy storage device

ABSTRACT

An ultracapacitor that includes an energy storage cell immersed in an electrolyte and disposed within an hermetically sealed housing, the cell electrically coupled to a positive contact and a negative contact, wherein the ultracapacitor is configured to output electrical energy within a temperature range between about 80 degrees Celsius to about 210 degrees Celsius. Methods of fabrication and use are provided.

The present application is a national stage filing under 35 U.S.C. § 371of international PCT application, PCT/US2012/045994, filed Jul. 9, 2012,which claims priority under 35 U.S.C. § 119(e) to U.S. ProvisionalApplication Ser. No. 61/619,203, filed Apr. 2, 2012, U.S. ProvisionalApplication Ser. No. 61/602,713, filed Feb. 24, 2012, U.S. ProvisionalApplication Ser. No. 61/569,010, filed Dec. 9, 2011, U.S. ProvisionalApplication Ser. No. 61/560,888, filed Nov. 17, 2011, U.S. ProvisionalApplication Ser. No. 61/512,090, filed Jul. 27, 2011, and U.S.Provisional Application Ser. No. 61/505,715, filed Jul. 8, 2011, eachone of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention disclosed herein relates to energy storage cells, and inparticular to techniques for providing an electric double-layercapacitor that is operable at high temperatures.

2. Description of the Related Art

Energy storage cells are ubiquitous in our society. While most peoplerecognize an energy storage cell simply as a “battery,” other types ofcells may be included. For example, recently, ultracapacitors havegarnered much attention as a result of their favorable characteristics.In short, many types of energy storage cells are known and in use today.

As a general rule, an energy storage cell includes an energy storagemedia disposed within a housing (such as a canister). While a metalliccanister can provide robust physical protection for the cell, such acanister is typically both electrically and thermally conductive and canreact with the energy storage cell. Typically, such reactions increasein rate as ambient temperature increases. The electrochemical or otherproperties of many canisters can cause poor initial performance and leadto premature degradation of the energy storage cell, especially atelevated temperatures.

In fact, a variety of factors work to degrade performance of energystorage systems at elevated temperatures. Thus, what are needed aremethods and apparatus for improving performance of an electricdouble-layer capacitor at elevated temperatures. Preferably, the methodsand apparatus result in improved performance at a minimal cost.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, an ultracapacitor is disclosed. The ultracapacitorincludes an energy storage cell immersed in an electrolyte and disposedwithin an hermetically sealed housing, the cell electrically coupled toa positive contact and a negative contact, wherein the ultracapacitor isconfigured to output electrical energy at a temperature within atemperature range between about 80 degrees Celsius to about 210 degreesCelsius.

In another embodiment, a method for fabricating an ultracapacitor isprovided. The method includes disposing an energy storage cell includingenergy storage media within a housing; and constructing theultracapacitor to operate within a temperature range between about 80degrees Celsius to about 210 degrees Celsius.

In yet another embodiment, a method for fabricating an ultracapacitor isprovided. The method includes disposing an energy storage cell includingenergy storage media within a housing; and filling the housing withelectrolyte adapted for operation within a temperature range betweenabout 80 degrees Celsius to about 210 degrees Celsius.

In a further embodiment, an ultracapacitor is disclosed. Theultracapacitor includes an energy storage cell wetted with anelectrolyte and disposed within a housing, wherein a level of moisturewithin the housing is no greater than about 1,000 parts per million(ppm) by combined weight of the storage cell and electrolyte.

In yet a further embodiment, an ultracapacitor is disclosed. Theultracapacitor includes an energy storage cell wetted with anelectrolyte and disposed within a housing, wherein a level of halideimpurities within the housing is no greater than 1,000 parts per millionby combined weight of the storage cell and electrolyte.

In another embodiment, a method for characterizing a contaminant withinan ultracapacitor is provided. The method includes breaching a housingof the ultracapacitor to access contents thereof; sampling the contents;and analyzing the sample.

In one embodiment, an ultracapacitor is disclosed. The ultracapacitorexhibits a volumetric leakage current (mA/cc) that is less than about 10mA/cc while held at a substantially constant temperature within a rangeof between about 100 degrees Celsius and about 150 degrees Celsius.

In one embodiment, an ultracapacitor is disclosed. The ultracapacitorexhibits a volumetric leakage current of less than about 10 mA/cc whileheld at a substantially constant temperature within a temperature rangeof between about 140 degrees Celsius and 180 degrees Celsius.

In one embodiment, an ultracapacitor is disclosed. The ultracapacitorexhibits a volumetric leakage current of less than about 10 mA/cc whileheld at a substantially constant temperature within a temperature rangeof between about 170 degrees Celsius and 210 degrees Celsius.

In another embodiment, a method for providing a high temperaturerechargeable energy storage device is disclosed. The method includesselecting a high temperature rechargeable energy storage device (HTRESD)that exhibits initial peak power density between 0.01 W/liter and 100kW/liter and a lifetime of at least 20 hours when exposed to an ambienttemperature in a temperature range from about 80 degrees Celsius toabout 210 degrees Celsius; and providing the storage device.

In another embodiment, a method for using a high temperaturerechargeable energy storage device is disclosed. The method includesobtaining an HTRESD and; at least one of cycling the HTRESD byalternatively charging and discharging the HTRESD at least twice over aduration of 20 hours, and maintaining a voltage across the HTRESD for 20hours, such that the HTRESD exhibits a peak power density between 0.005W/liter and 75 kW/liter after 20 hours when operated at an ambienttemperature that is in a temperature range of between about 80 degreesCelsius to about 210 degrees Celsius.

In another embodiment, a method for using a high temperaturerechargeable energy storage device is disclosed. The method includesobtaining an ultracapacitor and; maintaining a voltage across theultracapacitor, such that the ultracapacitor will exhibit a peak powerdensity of between about 0.005 W/liter and about 75 kW/liter after 20hours, wherein the ultracapacitor is exposed to an ambient temperaturein a temperature range from about 80 degrees Celsius to about 210degrees Celsius during the maintaining.

In another embodiment, a method for using an ultracapacitor isdisclosed. The method includes obtaining an ultracapacitor that has anelectrolyte and two electrodes, each of the electrodes in electricalcommunication with a current collector, and separated from the other bya separator; wherein one of charging and discharging the ultracapacitorprovides for an initial combination of peak power and energy densitiesin a range from about 0.1 Wh-kW/liter² to about 100 Wh-kW/liter²,wherein said combination is mathematically a product of the peak powerdensity and the energy density of the ultracapacitor; and wherein theultracapacitor exhibits a durability period of at least 20 hours whenexposed to an ambient temperature in a temperature range from about 80degrees Celsius to about 210 degrees Celsius, wherein the durability isindicated by a decrease in peak power density of no more than about 50percent over the period, and wherein the ultracapacitor is configured tocharged and discharged at least twice.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the invention areapparent from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 illustrates aspects of an exemplary ultracapacitor;

FIG. 2 is a block diagram depicting a plurality of carbon nanotubes(CNT) grown onto a substrate;

FIG. 3 is a block diagram depicting deposition of a current collectoronto the CNT of FIG. 3 to provide an electrode element;

FIG. 4 is a block diagram depicting addition of transfer tape to theelectrode element of FIG. 3;

FIG. 5 is a block diagram depicting the electrode element during atransfer process;

FIG. 6 is a block diagram depicting the electrode element subsequent totransfer;

FIG. 7 is a block diagram depicting an exemplary electrode fabricatedfrom a plurality of the electrode elements;

FIG. 8 depicts embodiments of primary structures for cations that may beincluded in the exemplary ultracapacitor;

FIGS. 9 and 10 provide comparative data for the exemplary ultracapacitormaking use of raw electrolyte and purified electrolyte, respectively;

FIG. 11 depicts an embodiment of a housing for the exemplaryultracapacitor;

FIG. 12 illustrates an embodiment of a storage cell for the exemplarycapacitor;

FIG. 13 depicts a barrier disposed on an interior portion of a body ofthe housing;

FIGS. 14A and 14B, collectively referred to herein as FIG. 14, depictaspects of a cap for the housing;

FIG. 15 depicts assembly of the ultracapacitor according to theteachings herein;

FIGS. 16A and 16B, collectively referred to herein as FIG. 16, aregraphs depicting performance for the ultracapacitor for an embodimentwithout a barrier and a similar embodiment that includes the barrier,respectively;

FIG. 17 depicts the barrier disposed about the storage cell as awrapper;

FIGS. 18A, 18B and 18C, collectively referred to herein as FIG. 18,depict embodiments of the cap that include multi-layered materials;

FIG. 19 is a cross-sectional view of an electrode assembly that includesa glass-to-metal seal;

FIG. 20 is a cross-sectional view of the electrode assembly of FIG. 19installed in the cap of FIG. 18B;

FIG. 21 depicts an arrangement of the energy storage cell in assembly;

FIGS. 22A, 22B and 22C, collectively referred to herein as FIG. 22,depict embodiments of an assembled energy storage cell;

FIG. 23 depicts incorporation of polymeric insulation into theultracapacitor;

FIGS. 24A, 24B and 24C, collectively referred to herein as FIG. 24,depict aspects of a template for another embodiment of the cap for theenergy storage;

FIG. 25 is a perspective view of an electrode assembly that includeshemispherically shaped material;

FIG. 26 is a perspective view of a cap including the electrode assemblyof FIG. 25 installed in the template of FIG. 24;

FIG. 27 is a cross-sectional view of the cap of FIG. 26;

FIG. 28 depicts coupling of the electrode assembly with a terminal of astorage cell;

FIG. 29 is a transparent isometric view of the energy storage celldisposed in a cylindrical housing;

FIG. 30 is a side view of the storage cell, showing the various layersof one embodiment;

FIG. 31 is an isometric view of a rolled up storage cell which includesa reference mark for placing a plurality of leads;

FIG. 32 is an isometric view of the storage cell of FIG. 31 onceunrolled;

FIG. 33 depicts the rolled up storage cell with the plurality of leadsincluded;

FIG. 34 depicts a Z-fold imparted into aligned leads (i.e., a terminal)coupled to the storage cell;

FIGS. 35-38 are graphs depicting performance of exemplaryultracapacitors; and

FIGS. 39-43 are graphs depicting performance of exemplaryultracapacitors at 210 degrees Celsius.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein is a capacitor that provides users with improvedperformance in a wide range of temperatures. For example, the capacitormay be operable at temperatures ranging from about as low as minus 40degrees Celsius to as high as about 210 degrees Celsius. In someembodiments, the capacitor is operable temperatures ranging from about80 degrees Celsius to as high as about 210 degrees Celsius.

In general, the capacitor includes energy storage media that is adaptedfor providing high power density and high energy density when comparedto prior art devices. The capacitor includes components that areconfigured for ensuring operation over the temperature range, andincludes any one or more of a variety of forms of electrolyte that arelikewise rated for the temperature range. The combination ofconstruction, energy storage media and electrolyte result incapabilities to provide robust operation under extreme conditions. Toprovide some perspective, aspects of an exemplary embodiment are nowintroduced.

As shown in FIG. 1, an exemplary embodiment of a capacitor is shown. Inthis case, the capacitor is an “ultracapacitor 10.” The exemplaryultracapacitor 10 is an electric double-layer capacitor (EDLC). The EDLCincludes at least one pair of electrodes 3 (where the electrodes 3 maybe referred to as a negative electrode 3 and a positive electrode 3,merely for purposes of referencing herein). When assembled into theultracapacitor 10, each of the electrodes 3 presents a double layer ofcharge at an electrolyte interface. In some embodiments, a plurality ofelectrodes 3 is included (for example, in some embodiments, at least twopairs of electrodes 3 are included). However, for purposes ofdiscussion, only one pair of electrodes 3 are shown. As a matter ofconvention herein, at least one of the electrodes 3 uses a carbon-basedenergy storage media 1 (as discussed further herein) to provide energystorage. However, for purposes of discussion herein, it is generallyassumed that each of the electrodes includes the carbon-based energystorage media 1. It should be noted that an electrolytic capacitordiffers from an ultracapacitor because metallic electrode differ greatly(at least an order of magnitude) in area.

Each of the electrodes 3 includes a respective current collector 2 (alsoreferred to as a “charge collector”). In some embodiments, theelectrodes 3 are separated by a separator 5. In general, the separator 5is a thin structural material (usually a sheet) used to separate thenegative electrode 3 from the positive electrode 3. The separator 5 mayalso serve to separate pairs of the electrodes 3. Once assembled, theelectrodes 3 and the separator 5 provide a storage cell 12. Note that,in some embodiments, the carbon-based energy storage media 1 may not beincluded on one or both of the electrodes 3. That is, in someembodiments, a respective electrode 3 might consist of only the currentcollector 2. The material used to provide the current collector 2 couldbe roughened, anodized or the like to increase a surface area thereof.In these embodiments, the current collector 2 alone may serve as theelectrode 3. With this in mind, however, as used herein, the term“electrode 3” generally refers to a combination of the energy storagemedia 1 and the current collector 2 (but this is not limiting, for atleast the foregoing reason).

At least one form of electrolyte 6 is included in the ultracapacitor 10.The electrolyte 6 fills void spaces in and between the electrodes 3 andthe separator 5. In general, the electrolyte 6 is a substance thatdisassociates into electrically charged ions. A solvent that dissolvesthe substance may be included in some embodiments of the electrolyte 6,as appropriate. The electrolyte 6 conducts electricity by ionictransport.

Generally, the storage cell 12 is formed into one of a wound form orprismatic form which is then packaged into a cylindrical or prismatichousing 7. Once the electrolyte 6 has been included, the housing 7 maybe hermetically sealed. In various examples, the package is hermeticallysealed by techniques making use of laser, ultrasonic, and/or weldingtechnologies. In addition to providing robust physical protection of thestorage cell 12, the housing 7 is configured with external contacts toprovide electrical communication with respective terminals 8 within thehousing 7. Each of the terminals 8, in turn, provides electrical accessto energy stored in the energy storage media 1, generally throughelectrical leads which are coupled to the energy storage media 1.

As discussed herein, “hermetic” refers to a seal whose quality (i.e.,leak rate) is defined in units of “atm-cc/second,” which means one cubiccentimeter of gas (e.g., He) per second at ambient atmospheric pressureand temperature. This is equivalent to an expression in units of“standard He-cc/sec.” Further, it is recognized that 1 atm-cc/sec isequal to 1.01325 mbar-liter/sec. Generally, the ultracapacitor 10disclosed herein is capable of providing a hermetic seal that has a leakrate no greater than about 5.0×10⁻⁶ atm-cc/sec, and may exhibit a leakrate no higher than about 5.0×10⁻¹° atm-cc/sec. It is also consideredthat performance of a successfully hermetic seal is to be judged by theuser, designer or manufacturer as appropriate, and that “hermetic”ultimately implies a standard that is to be defined by a user, designer,manufacturer or other interested party.

Leak detection may be accomplished, for example, by use of a tracer gas.Using tracer gas such as helium for leak testing is advantageous as itis a dry, fast, accurate and non destructive method. In one example ofthis technique, the ultracapacitor 10 is placed into an environment ofhelium. The ultracapacitor 10 is subjected to pressurized helium. Theultracapacitor 10 is then placed into a vacuum chamber that is connectedto a detector capable of monitoring helium presence (such as an atomicabsorption unit). With knowledge of pressurization time, pressure andinternal volume, the leak rate of the ultracapacitor 10 may bedetermined.

In some embodiments, at least one lead (which may also be referred toherein as a “tab”) is electrically coupled to a respective one of thecurrent collectors 2. A plurality of the leads (accordingly to apolarity of the ultracapacitor 10) may be grouped together and coupledto into a respective terminal 8. In turn, the terminal 8 may be coupledto an electrical access, referred to as a “contact” (e.g., one of thehousing 7 and an external electrode (also referred to herein forconvention as a “feed-through” or “pin”)). Reference may be had to FIGS.28 and 32-34. Consider now the energy storage media 1 in greater detail.

In the exemplary ultracapacitor 10, the energy storage media 1 is formedof carbon nanotubes. The energy storage media 1 may include othercarbonaceous materials including, for example, activated carbon, carbonfibers, rayon, graphene, aerogel, carbon cloth, and a plurality of formsof carbon nanotubes. Activated carbon electrodes can be manufactured,for example, by producing a carbon base material by carrying out a firstactivation treatment to a carbon material obtained by carbonization of acarbon compound, producing a formed body by adding a binder to thecarbon base material, carbonizing the formed body, and finally producingan active carbon electrode by carrying out a second activation treatmentto the carbonized formed body. Carbon fiber electrodes can be produced,for example, by using paper or cloth pre-form with high surface areacarbon fibers.

In an exemplary method for fabricating carbon nanotubes, an apparatusfor producing an aligned carbon-nanotube aggregate includes apparatusfor synthesizing the aligned carbon-nanotube aggregate on a basematerial having a catalyst on a surface thereof. The apparatus includesa formation unit that processes a formation step of causing anenvironment surrounding the catalyst to be an environment of a reducinggas and heating at least either the catalyst or the reducing gas; agrowth unit that processes a growth step of synthesizing the alignedcarbon-nanotube aggregate by causing the environment surrounding thecatalyst to be an environment of a raw material gas and by heating atleast either the catalyst or the raw material gas; and a transfer unitthat transfers the base material at least from the formation unit to thegrowth unit. A variety of other methods and apparatus may be employed toprovide the aligned carbon-nanotube aggregate.

In some embodiments, material used to form the energy storage media 1may include material other than pure carbon (and the various forms ofcarbon as may presently exist or be later devised). That is, variousformulations of other materials may be included in the energy storagemedia 1. More specifically, and as a non-limiting example, at least onebinder material may be used in the energy storage media 1, however, thisis not to suggest or require addition of other materials (such as thebinder material). In general, however, the energy storage media 1 issubstantially formed of carbon, and may therefore referred to herein asa “carbonaceous material,” as a “carbonaceous layer” and by othersimilar terms. In short, although formed predominantly of carbon, theenergy storage media 1 may include any form of carbon (as well as anyadditives or impurities as deemed appropriate or acceptable) to providefor desired functionality as energy storage media 1.

In one set of embodiments, the carbonaceous material includes at leastabout 60% elemental carbon by mass, and in other embodiments at leastabout 75%, 85%, 90%, 95% or 98% by mass elemental carbon.

Carbonaceous material can include carbon in a variety forms, includingcarbon black, graphite, and others. The carbonaceous material caninclude carbon particles, including nanoparticles, such as nanotubes,nanorods, graphene sheets in sheet form, and/or formed into cones, rods,spheres (buckyballs) and the like.

Some embodiments of various forms of carbonaceous material suited foruse in energy storage media 1 are provided herein as examples. Theseembodiments provide robust energy storage and are well suited for use inthe electrode 3. It should be noted that these examples are illustrativeand are not limiting of embodiments of carbonaceous material suited foruse in energy storage media 1.

In general, the term “electrode” refers to an electrical conductor thatis used to make contact to another material which is often non-metallic,in a device that may be incorporated into an electrical circuit.Generally, the term “electrode,” as used herein, is with reference tothe current collector 2 and the additional components as may accompanythe current collector 2 (such as the energy storage media 1) to providefor desired functionality (for example, the energy storage media 1 whichis mated to the current collector 2 to provide for energy storage andenergy transmission). An exemplary process for complimenting the energystorage media 1 with the current collector 2 to provide the electrode 3is now provided.

Referring now to FIG. 2, a substrate 14 that is host to carbonaceousmaterial in the form of carbon nanotube aggregate (CNT) is shown. In theembodiment shown, the substrate 14 includes a base material 17 with athin layer of a catalyst 18 disposed thereon.

In general, the substrate 14 is at least somewhat flexible (i.e., thesubstrate 14 is not brittle), and is fabricated from components that canwithstand environments for deposition of the energy storage media 1(e.g., CNT). For example, the substrate 14 may withstand ahigh-temperature environment of between about 400 degrees Celsius toabout 1,100 degrees Celsius. A variety of materials may be used for thesubstrate 14, as determined appropriate.

Refer now to FIG. 3. Once the energy storage media 1 (e.g., CNT) hasbeen fabricated on the substrate 14, the current collector 2 may bedisposed thereon. In some embodiments, the current collector 2 isbetween about 0.5 micrometers (μm) to about 25 micrometers (μm) thick.In some embodiments, the the current collector 2 is between about 20micrometers (μm) to about 40 micrometers (μm) thick. The currentcollector 2 may appear as a thin layer, such as layer that is applied bychemical vapor deposition (CVD), sputtering, e-beam, thermal evaporationor through another suitable technique. Generally, the current collector2 is selected for its properties such as conductivity, beingelectrochemically inert and compatible with the energy storage media 1(e.g., CNT). Some exemplary materials include aluminum, platinum, gold,tantalum, titanium, and may include other materials as well as variousalloys.

Once the current collector 2 is disposed onto the energy storage media 1(e.g., CNT), an electrode element 15 is realized. Each electrode element15 may be used individually as the electrode 3, or may be coupled to atleast another electrode element 15 to provide for the electrode 3.

Once the current collector 2 has been fabricated according to a desiredstandard, post-fabrication treatment may be undertaken. Exemplarypost-treatment includes heating and cooling of the energy storage media1 CNT) in a slightly oxidizing environment. Subsequent to fabrication(and optional post-treatment), a transfer tool may be applied to thecurrent collector 2. Reference may be had to FIG. 4.

FIG. 4 illustrates application of transfer tool 13 to the currentcollector 2. In this example, the transfer tool 13 is a thermal releasetape, used in a “dry” transfer method. Exemplary thermal release tape ismanufactured by NITTO DENKO CORPORATION of Fremont, Calif. and Osaka,Japan. One suitable transfer tape is marketed as REVALPHA. This releasetape may be characterized as an adhesive tape that adheres tightly atroom temperature and can be peeled off by heating. This tape, and othersuitable embodiments of thermal release tape, will release at apredetermined temperature. Advantageously, the release tape does notleave a chemically active residue on the electrode element 15.

In another process, referred to as a “wet” transfer method, tapedesigned for chemical release may be used. Once applied, the tape isthen removed by immersion in a solvent. The solvent is designed todissolve the adhesive.

In other embodiments, the transfer tool 13 uses a “pneumatic” method,such as by application of suction to the current collector 2. Thesuction may be applied, for example, through a slightly oversized paddlehaving a plurality of perforations for distributing the suction. Inanother example, the suction is applied through a roller having aplurality of perforations for distributing the suction. Suction drivenembodiments offer advantages of being electrically controlled andeconomic as consumable materials are not used as a part of the transferprocess. Other embodiments of the transfer tool 13 may be used.

Once the transfer tool 13 has been temporarily coupled to the currentcollector 2, the electrode element 15 is gently removed from thesubstrate 14 (see FIGS. 4 and 5). The removal generally involves peelingthe energy storage media 1 (e.g., CNT) from the substrate 14, beginningat one edge of the substrate 14 and energy storage media 1 (e.g., CNT).

Subsequently, the transfer tool 13 may be separated from the electrodeelement 15 (see FIG. 6). In some embodiments, the transfer tool 13 isused to install the electrode element 15. For example, the transfer tool13 may be used to place the electrode element 15 onto the separator 5.In general, once removed from the substrate 14, the electrode element 15is available for use.

In instances where a large electrode 3 is desired, a plurality of theelectrode elements 15 may be mated. Reference may be had to FIG. 7. Asshown in FIG. 7, a plurality of the electrode elements 15 may be matedby, for example, coupling a coupling 52 to each electrode element 15 ofthe plurality of electrode elements 15. The mated electrode elements 15provide for an embodiment of the electrode 3.

In some embodiments, the coupling 22 is coupled to each of the electrodeelements 15 at a weld 21. Each of the welds 21 may be provided as anultrasonic weld 21. It has been found that ultrasonic welding techniquesare particularly well suited to providing each weld 21. That is, ingeneral, the aggregate of energy storage media 1 (e.g., CNT) is notcompatible with welding, where only a nominal current collector, such asdisclosed herein is employed. As a result, many techniques for joiningelectrode elements 15 are disruptive, and damage the element 15.However, in other embodiments, other forms of coupling are used, and thecoupling 22 is not a weld 21.

The coupling 22 may be a foil, a mesh, a plurality of wires or in otherforms. Generally, the coupling 22 is selected for properties such asconductivity and being electrochemically inert. In some embodiments, thecoupling 22 is fabricated from the same material(s) as are present inthe current collector 2.

In some embodiments, the coupling 22 is prepared by removing an oxidelayer thereon. The oxide may be removed by, for example, etching thecoupling 22 before providing the weld 21. The etching may beaccomplished, for example, with potassium hydroxide (KOH). The electrode3 may be used in a variety of embodiments of the ultracapacitor 10. Forexample, the electrode 3 may be rolled up into a “jelly roll” type ofenergy storage.

The separator 5 may be fabricated from various materials. In someembodiments, the separator 5 is non-woven glass. The separator 5 mayalso be fabricated from fiberglass, ceramics and flouro-polymers, suchas polytetrafluoroethylene (PTFE), commonly marketed as TEFLON™ byDuPont Chemicals of Wilmington, Del. For example, using non-woven glass,the separator 5 can include main fibers and binder fibers each having afiber diameter smaller than that of each of the main fibers and allowingthe main fibers to be bonded together.

For longevity of the ultracapacitor 10 and to assure performance at hightemperature, the separator 5 should have a reduced amount of impuritiesand in particular, a very limited amount of moisture contained therein.In particular, it has been found that a limitation of about 200 ppm ofmoisture is desired to reduce chemical reactions and improve thelifetime of the ultracapacitor 10, and to provide for good performancein high temperature applications. Some embodiments of materials for usein the separator 5 include polyamide, polytetrafluoroethylene (PTFE),polyetheretherketone (PEEK), aluminum oxide (Al₂O₃), fiberglass, andglass-reinforced plastic (GRP).

In general, materials used for the separator 5 are chose according tomoisture content, porosity, melting point, impurity content, resultingelectrical performance, thickness, cost, availability and the like. Insome embodiments, the separator 5 is formed of hydrophobic materials.

Accordingly, procedures may be employed to ensure excess moisture iseliminated from each separator 5. Among other techniques, a vacuumdrying procedure may be used. A selection of materials for use in theseparator 5 is provided in Table 1. Some related performance data isprovided in Table 2.

TABLE 1 Separator Materials Melting PPM H₂O PPM H₂O Vacuum dry Materialpoint unbaked baked procedure Polyamide 256° C. 2052 20 180° C. for 24 hPolytetrafluoro- 327° C. 286 135 150° C. for 24 h ethylene, PTFEPolyether ether 256° C. 130 50 215° C. for 12 h ketone, PEEK AluminumOxide, 330° C. 1600 100 215° C. for 24 h Al₂O₃ Fiberglass (GRP) 320° C.2000 167 215° C. for 12 h

TABLE 2 Separator Performance Data ESR 1^(st) ESR 2^(nd) After 10Material μm Porosity test (Ω) test (Ω) CV Polyamide 42 Nonwoven 1.0691.069 1.213 PEEK 45 Mesh 1.665 1.675 2.160 PEEK 60% 25 60% 0.829 0.8400.883 Fiberglass (GRP) 160 Nonwoven 0.828 0.828 0.824 Aluminum 25 —2.400 2.400 2.400 Oxide, Al₂O₃

In order to collect data for Table 2, two electrodes 3, based oncarbonaceous material, were provided. The electrodes 3 were disposedopposite to and facing each other. Each of the separators 5 were placedbetween the electrodes 3 to prevent a short circuit. The threecomponents were then wetted with electrolyte 6 and compressed together.Two aluminum bars and PTFE material was used as an external structure toenclose the resulting ultracapacitor 10.

The ESR 1^(st) test and ESR 2^(nd) test were performed with the sameconfiguration one after the other. The second test was run five minutesafter the first test, leaving time for the electrolyte 6 to further soakinto the components.

Note that, in some embodiments, the ultracapacitor 10 does not requireor include the separator 5. For example, in some embodiments, such aswhere the electrodes 3 are assured of physical separation by a geometryof construction, it suffices to have electrolyte 6 alone between theelectrodes 3. More specifically, and as an example of physicalseparation, one such ultracapacitor 10 may include electrodes 3 that aredisposed within a housing such that separation is assured on acontinuous basis. A bench-top example would include an ultracapacitor 10provided in a beaker.

The ultracapacitor 10 may be embodied in several different form factors(i.e., exhibit a certain appearance). Examples of potentially usefulform factors include, a cylindrical cell, an annular or ring-shapedcell, a flat prismatic cell or a stack of flat prismatic cellscomprising a box-like cell, and a flat prismatic cell that is shaped toaccommodate a particular geometry such as a curved space. A cylindricalform factor may be most useful in conjunction with a cylindrical tool ora tool mounted in a cylindrical form factor. An annular or ring-shapedform factor may be most useful in conjunction with a tool that isring-shaped or mounted in a ring-shaped form factor. A flat prismaticcell shaped to accommodate a particular geometry may be useful to makeefficient use of “dead space” (i.e., space in a tool or equipment thatis otherwise unoccupied, and may be generally inaccessible).

While generally disclosed herein in terms of a “jelly roll” application(i.e., a storage cell 12 that is configured for a cylindrically shapedhousing 7), the rolled storage cell 23 may take any form desired. Forexample, as opposed to rolling the storage cell 12, folding of thestorage cell 12 may be performed to provide for the rolled storage cell23. Other types of assembly may be used. As one example, the storagecell 12 may be a flat cell, referred to as a “coin type” of cell.Accordingly, rolling is merely one option for assembly of the rolledstorage cell 23. Therefore, although discussed herein in terms of beinga “rolled storage cell 23”, this is not limiting. It may be consideredthat the term “rolled storage cell 23” generally includes anyappropriate form of packaging or packing the storage cell 12 to fit wellwithin a given design of the housing 7.

Various forms of the ultracapacitor 10 may be joined together. Thevarious forms may be joined using known techniques, such as weldingcontacts together, by use of at least one mechanical connector, byplacing contacts in electrical contact with each other and the like. Aplurality of the ultracapacitors 10 may be electrically connected in atleast one of a parallel and a series fashion.

The electrolyte 6 includes a pairing of cations 9 and anions 11 and mayinclude a solvent. The electrolyte 6 may be referred to as a “ionicliquid” as appropriate. Various combinations of cations 9, anions 11 andsolvent may be used. In the exemplary ultracapacitor 10, the cations 9may include at least one of 1-(3-Cyanopropyl)-3-methylimidazolium,1,2-Dimethyl-3-propylimidazolium, 1,3-Bis(3-cyanopropyl)imidazolium,1,3-Diethoxyimidazolium, 1-Butyl-1-methylpiperidinium,1-Butyl-2,3-dimethylimidazolium, 1-Butyl-3-methylimidazolium,1-Butyl-4-methylpyridinium, 1-Butylpyridinium,1-Decyl-3-methylimidazolium, 1-Ethyl-3-methylimidazolium,3-Methyl-1-propylpyridinium, and combinations thereof as well as otherequivalents as deemed appropriate. Additional exemplary cations 9include imidazolium, pyrazinium, piperidinium, pyridinium, pyrimidinium,and pyrrolidinium (structures of which are depicted in FIG. 8). In theexemplary ultracapacitor 10, the anions 11 may include at least one ofbis(trifluoromethanesulfonate)imide,tris(trifluoromethanesulfonate)methide, dicyanamide, tetrafluoroborate,hexafluorophosphate, trifluoromethanesulfonate,bis(pentafluoroethanesulfonate)imide, thiocyanate,trifluoro(trifluoromethyl)borate, and combinations thereof as well asother equivalents as deemed appropriate.

The solvent may include acetonitrile, amides, benzonitrile,butyrolactone, cyclic ether, dibutyl carbonate, diethyl carbonate,diethylether, dimethoxyethane, dimethyl carbonate, dimethylformamide,dimethylsulfone, dioxane, dioxolane, ethyl formate, ethylene carbonate,ethylmethyl carbonate, lactone, linear ether, methyl formate, methylpropionate, methyltetrahydrofuran, nitrile, nitrobenzene, nitromethane,n-methylpyrrolidone, propylene carbonate, sulfolane, sulfone,tetrahydrofuran, tetramethylene sulfone, thiophene, ethylene glycol,diethylene glycol, triethylene glycol, polyethylene glycols, carbonicacid ester, γ-butyrolactone, nitrile, tricyanohexane, any combinationthereof or other material(s) that exhibit appropriate performancecharacteristics.

Referring now to FIG. 8, there are shown various additional embodimentsof cations 9 suited for use in an ionic liquid to provide theelectrolyte 6. These cations 9 may be used alone or in combination witheach other, in combination with at least some of the foregoingembodiments of cations 9, and may also be used in combination with othercations 9 that are deemed compatible and appropriate by a user,designer, manufacturer or other similarly interested party. The cations9 depicted in FIG. 8 include, without limitation, ammonium, imidazolium,oxazolium, phosphonium, piperidinium, pyrazinium, pyrazinium,pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, sulfonium,thiazolium, triazolium, guanidium, isoquinolinium, benzotriazolium,viologen-types, and functionalized imidazolium cations.

With regard to the cations 9 shown in FIG. 8, various branch groups (R₁,R₂, R₃, . . . R_(x)) are included. In the case of the cations 9, eachbranch groups (R_(x)) may be one of alkyl, heteroalkyl, alkenyl,heteroalkenyl, alkynyl, heteroalkynyl, halo, amino, nitro, cyano,hydroxyl, sulfate, sulfonate, or a carbonyl group any of which isoptionally substituted.

The term “alkyl” is recognized in the art and may include saturatedaliphatic groups, including straight-chain alkyl groups, branched-chainalkyl groups, cycloalkyl (alicyclic) groups, alkyl substitutedcycloalkyl groups, and cycloalkyl substituted alkyl groups. In certainembodiments, a straight chain or branched chain alkyl has about 20 orfewer carbon atoms in its backbone (e.g., C₁-C₂₀ for straight chain,C₁-C₂₀ for branched chain). Likewise, cycloalkyls have from about 3 toabout 10 carbon atoms in their ring structure, and alternatively about5, 6 or 7 carbons in the ring structure. Examples of alkyl groupsinclude, but are not limited to, methyl, ethyl, propyl, butyl, pentyl,hexyl, ethyl hexyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl andthe like.

The term “heteroalkyl” is recognized in the art and refers to alkylgroups as described herein in which one or more atoms is a heteroatom(e.g., oxygen, nitrogen, sulfur, and the like). For example, alkoxygroup (e.g., —OR) is a heteroalkyl group.

The terms “alkenyl” and “alkynyl” are recognized in the art and refer tounsaturated aliphatic groups analogous in length and possiblesubstitution to the alkyls described above, but that contain at leastone double or triple bond respectively.

The “heteroalkenyl” and “heteroalkynyl” are recognized in the art andrefer to alkenyl and alkynyl alkyl groups as described herein in whichone or more atoms is a heteroatom (e.g., oxygen, nitrogen, sulfur, andthe like).

Generally, any ion with a negative charge maybe used as the anion 11.The anion 11 selected is generally paired with a large organic cation 9to form a low temperature melting ionic salt. Room temperature (andlower) melting salts come from mainly large anions 9 with a charge of−1. Salts that melt at even lower temperatures generally are realizedwith anions 11 with easily delocalized electrons. Anything that willdecrease the affinity between ions (distance, delocalization of charge)will subsequently decrease the melting point. Although possible anionformations are virtually infinite, only a subset of these will work inlow temperature ionic liquid application. This is a non-limitingoverview of possible anion formations for ionic liquids.

Common substitute groups (α) suited for use of the anions 11 provided inTable 3 include: —F⁻, —Cl⁻, —Br⁻, —I⁻, −OCH₃ ⁻, —CN⁻, —SCN⁻, —C₂H₃O₂ ⁻,—ClO⁻, —ClO₂ ⁻, —ClO₃ ⁻, —ClO₄ ⁻, —NCO⁻, —NCS⁻, —NCSe⁻, —NCN⁻,—OCH(CH₃)₂ ⁻, —CH₂OCH₃ ⁻, —COOH⁻, —OH⁻, —SOCH₃ ⁻, —SO₂CH₃ ⁻, —SOCH₃ ⁻,—SO₂CF₃ ⁻, —SO₃H⁻, —SO₃CF₃ ⁻, —O(CF₃)₂C₂(CF₃)₂O⁻, —CF₃ ⁻, —CHF₂ ⁻,—CH₂F⁻, —CH₃ ⁻—NO₃ ⁻, —NO₂ ⁻, —SO₃ ⁻, —SO₄ ²⁻, —SF₅ ⁻, —CB₁₁H₁₂ ⁻,—CB₁₁H₆C₁₆ ⁻, —CH₃CB₁₁H₁₁ ⁻, —C₂H₅CB₁₁H₁₁ ⁻, -A-PO₄ ⁻, -A-SO₂ ⁻, A-SO₃⁻, -A-SO₃H⁻, -A-COO⁻, -A-CO⁻ 55 where A is a phenyl (the phenyl group orphenyl ring is a cyclic group of atoms with the formula C₆H₅) orsubstituted phenyl, alkyl, (a radical that has the general formulaCnH_(2n+1), formed by removing a hydrogen atom from an alkane) orsubstituted alkyl group, negatively charged radical alkanes, (alkane arechemical compounds that consist only of hydrogen and carbon atoms andare bonded exclusively by single bonds) halogenated alkanes and ethers(which are a class of organic compounds that contain an oxygen atomconnected to two alkyl or aryl groups).

With regard to anions 11 suited for use in an ionic liquid that providesthe electrolyte 6, various organic anions 11 may be used. Exemplaryanions 11 and structures thereof are provided in Table 3. In a firstembodiment, (No. 1), exemplary anions 11 are formulated from the list ofsubstitute groups (α) provided above, or their equivalent. In additionalembodiments, (Nos. 2-5), exemplary anions 11 are formulated from arespective base structure (Y₂, Y₃, Y₄, . . . Y_(n)) and a respectivenumber of anion substitute groups (α₁, α₂, α₃, . . . α_(n)), where therespective number of anion substitute groups (α) may be selected fromthe list of substitute (α) groups provided above, or their equivalent.Note that in some embodiments, a plurality of anion substitute groups(α) (i.e., at least one differing anion substitute group (α)) may beused in any one embodiment of the anion 11. Also, note that in someembodiments, the base structure (Y) is a single atom or a designatedmolecule (as described in Table 3), or may be an equivalent.

More specifically, and by way of example, with regard to the exemplaryanions provided in Table 3, certain combinations may be realized. As oneexample, in the case of No. 2, the base structure (Y₂) includes a singlestructure (e.g., an atom, or a molecule) that is bonded to two anionsubstitute groups (α₂). While shown as having two identical anionsubstitute groups (α₂), this need not be the case. That is, the basestructure (Y₂) may be bonded to varying anion substitute groups (α₂),such as any of the anion substitute groups (α) listed above. Similarly,the base structure (Y₃) includes a single structure (e.g., an atom) thatis bonded to three anion substitute groups (α₃), as shown in case No. 3.Again, each of the anion substitute groups (α) included in the anion maybe varied or diverse, and need not repeat (be repetitive or besymmetric) as shown in Table 3. In general, with regard to the notationin Table 3, a subscript on one of the base structures denotes a numberof bonds that the respective base structure may have with anionsubstitute groups (α). That is, the subscript on the respective basestructure (Y_(n)) denotes a number of accompanying anion substitutegroups (α_(n)) in the respective anion.

TABLE 3 Exemplary Organic Anions for an Ionic Liquid Guidelines forAnion Structure and Exemplary No.: Ion Ionic Liquids 1 −α₁ Some of theabove α may mix with organic cations to form an ionic liquid. Anexemplary anion: Cl⁻ Exemplary ionic liquid: [BMI*] [Cl] *BMI—butylmethyl immadizolium

2 −Y₂α₂ Y₂ may be any of the following: N, O, C═O, S═O. Exemplary anionsinclude: B (CF₃C0₂)₄ ⁻N(SO₂CF₃)₂ ⁻ Exemplary ionic liquid: [EMI*][NTF₂]*EMI—ethyl methyl immadizolium

3 −Y₃α₃ Y₃ may be any of the following: Be, C, N, O, Mg, Ca, Ba, Ra, Au.Exemplary anions include: −C(SO₂CF₃)₃ ⁻ Exemplary ionic liquid: [BMI]C(SO₂CF₃)₃ ⁻

4 −Y₄α₄ Y₄ may be any of the following: B, Al, Ga, Th, In, P. Exemplaryanions include: −BF₄ ⁻, −AlCl₄ ⁻ Exemplary ionic liquid: [BMI][BF₄]

5 −Y₆α₆ Y₆ can be any of the following: P, S, Sb, As, N, Bi, Nb, Sb.Exemplary anions include: −P(CF₃)₄F₂ ⁻, −AsF₆ ⁻ Exemplary ionic liquid:[BMI][PF₆]

The term “cyano” is given its ordinary meaning in the art and refers tothe group, CN. The term “sulfate” is given its ordinary meaning in theart and refers to the group, SO₂. The term “sulfonate” is given itsordinary meaning in the art and refers to the group, SO₃X, where X maybe an electron pair, hydrogen, alkyl or cycloalkyl. The term “carbonyl”is recognized in the art and refers to the group, C═O.

An important aspect for consideration in construction of theultracapacitor 10 is maintaining good chemical hygiene. In order toassure purity of the components, in various embodiments, the activatedcarbon, carbon fibers, rayon, carbon cloth, and/or nanotubes making upthe energy storage media 1 for the two electrodes 3, are dried atelevated temperature in a vacuum environment. The separator 5 is alsodried at elevated temperature in a vacuum environment. Once theelectrodes 3 and the separator 5 are dried under vacuum, they arepackaged in the housing 7 without a final seal or cap in an atmospherewith less than 50 parts per million (ppm) of water. The uncappedultracapacitor 10 may be dried, for example, under vacuum over atemperature range of about 100 degrees Celsius to about 300 degreesCelsius. Once this final drying is complete, the electrolyte 6 may beadded and the housing 7 is sealed in a relatively dry atmosphere (suchas an atmosphere with less than about 50 ppm of moisture). Of course,other methods of assembly may be used, and the foregoing provides merelya few exemplary aspects of assembly of the ultracapacitor 10.

Generally, impurities in the electrolyte 6 are kept to a minimum. Forexample, in some embodiments, a total concentration of halide ions(chloride, bromide, fluoride, iodide), is kept to below about 1,000 ppm.A total concentration of metallic species (e.g., Br, Cd, Co, Cr, Cu, Fe,K, Li, Mo, Na, Ni, Pb, Zn, including an at least one of an alloy and anoxide thereof), is kept to below about 1,000 ppm. Further, impuritiesfrom solvents and precursors used in the synthesis process are keptbelow about 1,000 ppm and can include, for example, bromoethane,chloroethane, 1-bromobutane, 1-chlorobutane, 1-methylimidazole, ethylacetate, methylene chloride and so forth.

In some embodiments, the impurity content of the ultracapacitor 10 hasbeen measured using ion selective electrodes and the Karl Fischertitration procedure, which has been applied to electrolyte 6 of theultracapacitor 10. It has been found that the total halide content inthe ultracapacitor 10 according to the teachings herein has been foundto be less than about 200 ppm of halides (Cl⁻ and F⁻) and water contentis less than about 100 ppm.

One example of a technique for purifying electrolyte is provided in areference entitled “The oxidation of alcohols in substituted imidazoliumionic liquids using ruthenium catalysts,” Farmer and Welton, The RoyalSociety of Chemistry, 2002, 4, 97-102. An exemplary process is alsoprovided herein.

Impurities can be measured using a variety of techniques, such as, forexample, Atomic Absorption Spectometry (AAS), Inductively CoupledPlasma-Mass Spectometry (ICPMS), or simplified solubilizing andelectrochemical sensing of trace heavy metal oxide particulates. AAS isa spectro-analytical procedure for the qualitative and quantitativedetermination of chemical elements employing the absorption of opticalradiation (light) by free atoms in the gaseous state. The technique isused for determining the concentration of a particular element (theanalyte) in a sample to be analyzed. AAS can be used to determine overseventy different elements in solution or directly in solid samples.ICPMS is a type of mass spectrometry that is highly sensitive andcapable of the determination of a range of metals and several non-metalsat concentrations below one part in 10¹² (part per trillion). Thistechnique is based on coupling together an inductively coupled plasma asa method of producing ions (ionization) with a mass spectrometer as amethod of separating and detecting the ions. ICPMS is also capable ofmonitoring isotopic specification for the ions of choice.

Additional techniques may be used for analysis of impurities. Some ofthese techniques are particularly advantageous for analyzing impuritiesin solid samples. Ion Chromatography (IC) may be used for determinationof trace levels of halide impurities in the electrolyte 6 (e.g., anionic liquid). One advantage of Ion Chromatography is that relevanthalide species can be measured in a single chromatographic analysis. ADionex AS9-HC column using an eluent consisting 20 mM NaOH and 10% (v/v)acetonitrile is one example of an apparatus that may be used for thequantification of halides from the ionic liquids. A further technique isthat of X-ray fluorescence.

X-ray fluorescence (XRF) instruments may be used to measure halogencontent in solid samples. In this technique, the sample to be analyzedis placed in a sample cup and the sample cup is then placed in theanalyzer where it is irradiated with X-rays of a specific wavelength.Any halogen atoms in the sample absorb a portion of the X-rays and thenreflect radiation at a wavelength that is characteristic for a givenhalogen. A detector in the instrument then quantifies the amount ofradiation coming back from the halogen atoms and measures the intensityof radiation. By knowing the surface area that is exposed, concentrationof halogens in the sample can be determined. A further technique forassessing impurities in a solid sample is that of pyrolysis.

Adsorption of impurities may be effectively measured through use ofpyrolysis and microcoulometers. Microcoulometers are capable of testingalmost any type of material for total chlorine content. As an example, asmall amount of sample (less than 10 milligrams) is either injected orplaced into a quartz combustion tube where the temperature ranges fromabout 600 degrees Celsius to about 1,000 degrees Celsius. Pure oxygen ispassed through the quartz tube and any chlorine containing componentsare combusted completely. The resulting combustion products are sweptinto a titration cell where the chloride ions are trapped in anelectrolyte solution. The electrolyte solution contains silver ions thatimmediately combine with any chloride ions and drop out of solution asinsoluble silver chloride. A silver electrode in the titration cellelectrically replaces the used up silver ions until the concentration ofsilver ions is back to where it was before the titration began. Bykeeping track of the amount of current needed to generate the requiredamount of silver, the instrument is capable of determining how muchchlorine was present in the original sample. Dividing the total amountof chlorine present by the weight of the sample gives the concentrationof chlorine that is actually in the sample. Other techniques forassessing impurities may be used.

Surface characterization and water content in the electrode 3 may beexamined, for example, by infrared spectroscopy techniques. The fourmajor absorption bands at around 1130, 1560, 3250 and 2300 cm⁻¹,correspond to νC═O in, νC═C in aryl, νO—H and νC—N, respectively. Bymeasuring the intensity and peak position, it is possible toquantitatively identify the surface impurities within the electrode 3.

Another technique for identifying impurities in the electrolyte 6 andthe ultracapacitor 10 is Raman spectroscopy. This spectroscopictechnique relies on inelastic scattering, or Raman scattering, ofmonochromatic light, usually from a laser in the visible, near infrared,or near ultraviolet range. The laser light interacts with molecularvibrations, phonons or other excitations in the system, resulting in theenergy of the laser photons being shifted up or down. Thus, thistechnique may be used to characterize atoms and molecules within theultracapacitor 10. A number of variations of Raman spectroscopy areused, and may prove useful in characterizing contents the ultracapacitor10.

Once the ultracapacitor 10 is fabricated, it may be used in hightemperature applications with little or no leakage current and littleincrease in resistance. The ultracapacitor 10 described herein canoperate efficiently at temperatures from about minus 40 degrees Celsiusto about 210 degrees Celsius with leakage currents normalized over thevolume of the device less than 1 amp per liter (A/L) of volume of thedevice within the entire operating voltage and temperature range.

By reducing the moisture content in the ultracapacitor 10 (e.g., to lessthan 500 part per million (ppm) over the weight and volume of theelectrolyte and the impurities to less than 1,000 ppm), theultracapacitor 10 can efficiently operate over the temperature range,with a leakage current (I/L) that is less than 1,000 mAmp per Literwithin that temperature range and voltage range.

In one embodiment, leakage current (I/L) at a specific temperature ismeasured by holding the voltage of the ultracapacitor 10 constant at therated voltage (i.e., the maximum rated operating voltage) for seventytwo (72) hours. During this period, the temperature remains relativelyconstant at the specified temperature. At the end of the measurementinterval, the leakage current of the ultracapacitor 10 is measured.

In some embodiments, a maximum voltage rating of the ultracapacitor 10is about 4 V at room temperature. An approach to ensure performance ofthe ultracapacitor 10 at elevated temperatures (for example, over 210degrees Celsius), is to derate (i.e., to reduce) the voltage rating ofthe ultracapacitor 10. For example, the voltage rating may be adjusteddown to about 0.5 V, such that extended durations of operation at highertemperature are achievable.

Another embodiment for ensuring a high degree of purity includes anexemplary process for purifying the electrolyte 6. It should be notedthat although the process is presented in terms of specific parameters(such as quantities, formulations, times and the like), that thepresentation is merely exemplary and illustrative of the process forpurifying electrolyte and is not limiting thereof.

In a first step of the process for purifying electrolyte, theelectrolyte 6 (in some embodiments, the ionic liquid) is mixed withdeionized water, and then raised to a moderate temperature for someperiod of time. In a proof of concept, fifty (50) milliliters (ml) ofionic liquid was mixed with eight hundred and fifty (850) milliliters(ml) of the deionized water. The mixture was raised to a constanttemperature of sixty (60) degrees Celsius for about twelve (12) hoursand subjected to constant stirring (of about one hundred and twenty(120) revolutions per minute (rpm)).

In a second step, the mixture of ionic liquid and deionized water ispermitted to partition. In this example, the mixture was transferred viaa funnel, and allowed to sit for about four (4) hours.

In a third step, the ionic liquid is collected. In this example, a waterphase of the mixture resided on the bottom, with an ionic liquid phaseon the top. The ionic liquid phase was transferred into another beaker.

In a fourth step, a solvent was mixed with the ionic liquid. In thisexample, a volume of about twenty five (25) milliliters (ml) of ethylacetate was mixed with the ionic liquid. This mixture was again raisedto a moderate temperature and stirred for some time.

Although ethyl acetate was used as the solvent, the solvent can be atleast one of diethylether, pentone, cyclopentone, hexane, cyclohexane,benzene, toluene, 1-4 dioxane, chloroform or any combination thereof aswell as other material(s) that exhibit appropriate performancecharacteristics. Some of the desired performance characteristics includethose of a non-polar solvent as well as a high degree of volatility.

In a fifth step, carbon powder is added to the mixture of the ionicliquid and solvent. In this example, about twenty (20) weight percent(wt %) of carbon (of about a 0.45 micrometer diameter) was added to themixture.

In a sixth step, the ionic liquid is again mixed. In this example, themixture with the carbon powder was then subjected to constant stirring(120 rpm) overnight at about seventy (70) degrees Celsius.

In a seventh step, the carbon and the ethyl acetate are separated fromthe ionic liquid. In this example, the carbon was separated usingBuchner filtration with a glass microfiber filter. Multiple filtrations(three) were performed. The ionic liquid collected was then passedthrough a 0.2 micrometer syringe filter in order to remove substantiallyall of the carbon particles. In this example, the solvent was thensubsequently separated from the ionic liquid by employing rotaryevaporation. Specifically, the sample of ionic liquid was stirred whileincreasing temperature from seventy (70) degrees Celsius to eighty (80)degrees Celsius, and finished at one hundred (100) degrees Celsius.Evaporation was performed for about fifteen (15) minutes at each of therespective temperatures.

The process for purifying electrolyte has proven to be very effective.For the sample ionic liquid, water content was measured by titration,with a titration instrument provided by Mettler-Toledo Inc., ofColumbus, Ohio (model No: AQC22). Halide content was measured with anISE instrument provided by Hanna Instruments of Woonsocket, R.I. (modelno. AQC22). The standards solution for the ISE instrument was obtainedfrom Hanna, and included HI 4007-03 (1,000 ppm chloride standard), HI4010-03 (1,000 ppm fluoride standard) HI 4000-00 (ISA for halideelectrodes), and HI 4010-00 (TISAB solution for fluoride electrodeonly). Prior to performing measurements, the ISE instrument wascalibrated with the standards solutions using 0.1, 10, 100 and 1,000parts per million (ppm) of the standards, mixed in with deionized water.ISA buffer was added to the standard in a 1:50 ratio for measurement ofCl⁻ ions. Results are shown in Table 4.

TABLE 4 Purification Data for Electrolyte Before After Impurity (ppm)(ppm) Cl⁻ 5,300.90 769 F− 75.61 10.61 H₂0 1080 20

A four step process was used to measure the halide ions. First, Cl⁻ andF ions were measured in the deionized water. Next, a 0.01 M solution ofionic liquid was prepared with deionized water. Subsequently, Cl⁻ and Fions were measured in the solution. Estimation of the halide content wasthen determined by subtracting the quantity of ions in the water fromthe quantity of ions in the solution.

As an overview, a method of assembly of a cylindrically shapedultracapacitor 10 is provided. Beginning with the electrodes 3, eachelectrode 3 is fabricated once the energy storage media 1 has beenassociated with the current collector 2. A plurality of leads are thencoupled to each electrode 3 at appropriate locations. A plurality ofelectrodes 3 are then oriented and assembled with an appropriate numberof separators 5 therebetween to form the storage cell 12. The storagecell 12 may then be rolled into a cylinder, and may be secured with awrapper. Generally, respective ones of the leads are then bundled toform each of the terminals 8.

Prior to incorporation of the electrolyte 6 into the ultracapacitor 10(such as prior to assembly of the storage cell 12, or thereafter) eachcomponent of the ultracapacitor 10 may be dried to remove moisture. Thismay be performed with unassembled components (i.e., an empty housing 7,as well as each of the electrodes 3 and each of the separators 5), andsubsequently with assembled components (such as the storage cell 12).

Drying may be performed, for example, at an elevated temperature in avacuum environment. Once drying has been performed, the storage cell 12may then be packaged in the housing 7 without a final seal or cap. Insome embodiments, the packaging is performed in an atmosphere with lessthan 50 parts per million (ppm) of water. The uncapped ultracapacitor 10may then be dried again. For example, the ultracapacitor 10 may be driedunder vacuum over a temperature range of about 100 degrees Celsius toabout 300 degrees Celsius. Once this final drying is complete, thehousing 7 may then be sealed in, for example, an atmosphere with lessthan 50 ppm of moisture.

In some embodiments, once the drying process (which may also be referredto a “baking” process) has been completed, the environment surroundingthe components may be filled with an inert gas. Exemplary gasses includeargon, nitrogen, helium, and other gasses exhibiting similar properties(as well as combinations thereof).

Generally, a fill port (a perforation in a surface of the housing 7) isincluded in the housing 7, or may be later added. Once theultracapacitor 10 has been filled with electrolyte 6, the fill port maythen be closed. Closing the fill port may be completed, for example, bywelding material (e.g., a metal that is compatible with the housing 7)into or over the fill port. In some embodiments, the fill port may betemporarily closed prior to filling, such that the ultracapacitor 10 maybe moved to another environment, for subsequent re-opening, filling andclosure. However, as discussed herein, it is considered that theultracapacitor 10 is dried and filled in the same environment.

A number of methods may be used to fill the housing 7 with a desiredquantity of electrolyte 6. Generally, controlling the fill process mayprovide for, among other things, increases in capacitance, reductions inequivalent-series-resistance (ESR), and limiting waste of electrolyte 6.A vacuum filling method is provided as a non-limiting example of atechnique for filling the housing 7 and wetting the storage cell 12 withthe electrolyte 6.

First, however, note that measures may be taken to ensure that anymaterial that has a potential to contaminate components of theultracapacitor 10 is clean, compatible and dry. As a matter ofconvention, it may be considered that “good hygiene” is practiced toensure assembly processes and components do not introduce contaminantsinto the ultracapacitor 10. Also, as a matter of convention, it may beconsidered that a “contaminant” may be defined as any unwanted materialthat will negatively affect performance of the ultracapacitor 10 ifintroduced. Also note, that generally herein, contaminants may beassessed as a concentration, such as in parts-per-million (ppm). Theconcentration may be taken as by weight, volume, sample weight, or inany other manner as determined appropriate.

In the “vacuum method” a container is placed onto the housing 7 aroundthe fill port. A quantity of electrolyte 6 is then placed into thecontainer in an environment that is substantially free of oxygen andwater (i.e., moisture). A vacuum is then drawn in the environment, thuspulling any air out of the housing and thus simultaneously drawing theelectrolyte 6 into the housing 7. The surrounding environment may thenbe refilled with inert gas (such as argon, nitrogen, or the like, orsome combination of inert gases), if desired. The ultracapacitor 10 maybe checked to see if the desired amount of electrolyte 6 has been drawnin. The process may be repeated as necessary until the desired amount ofelectrolyte 6 is in the ultracapacitor 10.

After filling with electrolyte 6, in some embodiments, material may befit into the fill port to seal the ultracapacitor 10. The material maybe, for example, a metal that is compatible with the housing 7 and theelectrolyte 6. In one example, material is force fit into the fill port,essentially performing a “cold weld” of a plug in the fill port. Ofcourse, the force fit may be complimented with other welding techniquesas discussed further herein.

In order to show how the fill process effects the ultracapacitor 10, twosimilar embodiments of the ultracapacitor 10 were built. One was filledwithout a vacuum, the other was filled under vacuum. Electricalperformance of the two embodiments is provided in Table 5. By repeatedperformance of such measurements, it has been noted that increasedperformance is realized with by filling the ultracapacitor 10 throughapplying a vacuum. It has been determined that, in general, is desiredthat pressure within the housing 7 is reduced to below about 150 mTorr,and more particularly to below about 40 mTorr.

TABLE 5 Comparative Performance for Fill Methods Parameter Without With(at 0.1 V) vacuum vacuum Deviation ESR @ 45° Φ 3.569 Ohms 2.568 Ohms (−28%) Capacitance @ 155.87 mF 182.3 mF (+14.49%)  12 mHz Phase @ 12mHz 79.19 degrees 83 degrees (+4.59%)

In order to evaluate efficacy of vacuum filling techniques, twodifferent pouch cells were tested. The pouch cells included twoelectrodes 3, each electrode 3 being based on carbonaceous material.Each of the electrodes 3 were placed opposite and facing each other. Theseparator 5 was disposed between them to prevent short circuit andeverything was soaked in electrolyte 6. Two external tabs were used toprovide for four measurement points. The separator 5′ used was apolyethylene separator 5, and the cell had a total volume of about 0.468ml.

FIG. 9 depicts leakage current for unpurified electrolyte in theultracapacitor 10. FIG. 10 depicts leakage current for purifiedelectrolyte in a similarly structured ultracapacitor 10. As one can see,there is a substantial decrease in initial leakage current, as well as adecrease in leakage current over the later portion of the measurementinterval. More information is provided on the construction of eachembodiment in Table 6.

TABLE 6 Test Ultracapacitor Configuration Parameter FIG. 9 FIG. 10 CellSize: Open Sub C Open Sub C Casing: Coated with PTFE Coated with PTFEElectrode: Carbonaceous Carbonaceous Separator: Fiberglass FiberglassLeads: 0.005″ Aluminum (3 leads) 0.005″ Aluminum (3 leads) Temperature150 degrees Celsius 150 degrees Celsius Electrolyte: Unpurified Purified

Leakage current may be determined in a number of ways. Qualitatively,leakage current may be considered as current drawn into a device, oncethe device has reached a state of equilibrium. In practice, it is alwaysor almost always necessary to estimate the actual leakage current as astate of equilibrium that may generally only by asymptoticallyapproached. Thus, the leakage current in a given measurement may beapproximated by measuring the current drawn into the ultracapacitor 10,while the ultracapacitor 10 is held at a substantially fixed voltage andexposed to a substantially fixed ambient temperature for a relativelylong period of time. In some instances, a relatively long period of timemay be determined by approximating the current time function as anexponential function, then allowing for several (e.g, about 3 to 5)characteristic time constants to pass. Often, such a duration rangesfrom about 50 hours to about 100 hours for many ultracapacitortechnologies. Alternatively, if such a long period of time isimpractical for any reason, the leakage current may simply beextrapolated, again, perhaps, by approximating the current time functionas an exponential or any approximating function deemed appropriate.Notably, leakage current will generally depend on ambient temperature.So, in order to characterize performance of a device at a temperature orin a temperature range, it is generally important to expose the deviceto the ambient temperature of interest when measuring leakage current.

Refer now to FIG. 11, where aspects of an exemplary housing 7 are shown.Among other things, the housing 7 provides structure and physicalprotection for the ultracapacitor 10. In this example, the housing 7includes an annular cylindrically shaped body 20 and a complimentary cap24. In this embodiment, the cap 24 includes a central portion that hasbeen removed and filled with an electrical insulator 26. A capfeed-through 19 penetrates through the electrical insulator 26 toprovide users with access to the stored energy.

Common materials for the housing 7 include stainless steel, aluminum,tantalum, titanium, nickel, copper, tin, various alloys, laminates, andthe like. Structural materials, such as some polymer-based materials maybe used in the housing 7 (generally in combination with at least somemetallic components).

Although this example depicts only one feed-through 19 on the cap 24, itshould be recognized that the construction of the housing 7 is notlimited by the embodiments discussed herein. For example, the cap 24 mayinclude a plurality of feed-throughs 19. In some embodiments, the body20 includes a second, similar cap 24 at an opposing end of the annularcylinder. Further, it should be recognized that the housing 7 is notlimited to embodiments having an annular cylindrically shaped body 20.For example, the housing 7 may be a clamshell design, a prismaticdesign, a pouch, or of any other design that is appropriate for theneeds of the designer, manufacturer or user.

In this example, the cap 24 is fabricated with an outer diameter that isdesigned for fitting snugly within an inner diameter of the body 20.When assembled, the cap 24 may be welded into the body 20, thusproviding users with a hermetic seal.

Referring now to FIG. 12, there is shown an exemplary energy storagecell 12. In this example, the energy storage cell 12 is a “jelly roll”type of energy storage. In these embodiments, the energy storagematerials are rolled up into a tight package. A plurality of leadsgenerally form each terminal 8 and provide electrical access to theappropriate layer of the energy storage cell 12. Generally, whenassembled, each terminal 8 is electrically coupled to the housing 7(such as to a respective feed-through 19 and/or directly to the housing7). The energy storage cell 12 may assume a variety of forms. There aregenerally at least two plurality of leads (e.g., terminals 8), one foreach current collector 2. For simplicity, only one of terminal 8 isshown in FIGS. 12, 15 and 17.

A highly efficient seal of the housing 7 is desired. That is, preventingintrusion of the external environment (such as air, humidity, etc, . . .) helps to maintain purity of the components of the energy storage cell12. Further, this prevents leakage of electrolyte 6 from the energystorage cell 12.

Referring now to FIG. 13, the housing 7 may include an inner barrier 30.In some embodiments, the barrier 30 is a coating. In this example, thebarrier 30 is formed of polytetrafluoroethylene (PTFE).Polytetrafluoroethylene (PTFE) exhibits various properties that makethis composition well suited for the barrier 30. FIFE has a meltingpoint of about 327 degrees Celsius, has excellent dielectric properties,has a coefficient of friction of between about 0.05 to 0.10, which isthe third-lowest of any known solid material, has a high corrosionresistance and other beneficial properties. Generally, an interiorportion of the cap 24 may include the barrier 30 disposed thereon.

Other materials may be used for the barrier 30. Among these othermaterials are forms of ceramics (any type of ceramic that may besuitably applied and meet performance criteria), other polymers(preferably, a high temperature polymer) and the like. Exemplary otherpolymers include perfluoroalkoxy (PFA) and fluorinated ethylenepropylene (FEP) as well as ethylene tetrafluoroethylene (ETFE).

The barrier 30 may include any material or combinations of materialsthat provide for reductions in electrochemical or other types ofreactions between the energy storage cell 12 and the housing 7 orcomponents of the housing 7. In some embodiments, the combinations aremanifested as homogeneous dispersions of differing materials within asingle layer. In other embodiments, the combinations are manifested asdiffering materials within a plurality of layers. Other combinations maybe used. In short, the barrier 30 may be considered as at least one ofan electrical insulator and chemically inert (i.e., exhibiting lowreactivity) and therefore substantially resists or impedes at least oneof electrical and chemical interactions between the storage cell 12 andthe housing 7. In some embodiments, the term “low reactivity” and “lowchemical reactivity” generally refer to a rate of chemical interactionthat is below a level of concern for an interested party.

In general, the interior of the housing 7 may be host to the barrier 30such that all surfaces of the housing 7 which are exposed to theinterior are covered. At least one untreated area 31 may be includedwithin the body 20 and on an outer surface 36 of the cap 24 (see FIG.14A). In some embodiments, untreated areas 31 (see FIG. 14B) may beincluded to account for assembly requirements, such as areas which willbe sealed or connected (such as by welding).

The barrier 30 may be applied to the interior portions usingconventional techniques. For example, in the case of PTFE, the barrier30 may be applied by painting or spraying the barrier 30 onto theinterior surface as a coating. A mask may be used as a part of theprocess to ensure untreated areas 31 retain desired integrity. In short,a variety of techniques may be used to provide the barrier 30.

In an exemplary embodiment, the barrier 30 is about 3 mil to about 5 milthick, while material used for the barrier 30 is a PFA based material.In this example, surfaces for receiving the material that make up thebarrier 30 are prepared with grit blasting, such as with aluminum oxide.Once the surfaces are cleaned, the material is applied, first as aliquid then as a powder. The material is cured by a heat treatingprocess. In some embodiments, the heating cycle is about 10 minutes toabout 15 minutes in duration, at temperatures of about 370 degreesCelsius. This results in a continuous finish to the barrier 30 that issubstantially free of pin-hole sized or smaller defects. FIG. 15 depictsassembly of an embodiment of the ultracapacitor 10 according to theteachings herein. In this embodiment, the ultracapacitor 10 includes thebody 20 that includes the barrier 30 disposed therein, a cap 24 with thebarrier 30 disposed therein, and the energy storage cell 12. Duringassembly, the cap 24 is set over the body 20. A first one of theterminals 8 is electrically coupled to the cap feed-through 19, while asecond one of the terminals 8 is electrically coupled to the housing 7,typically at the bottom, on the side or on the cap 24. In someembodiments, the second one of the terminals 8 is coupled to anotherfeed-through 19 (such as of an opposing cap 24).

With the barrier 30 disposed on the interior surface(s) of the housing7, electrochemical and other reactions between the housing 7 and theelectrolyte are greatly reduced or substantially eliminated. This isparticularly significant at higher temperatures where a rate of chemicaland other reactions is generally increased.

Referring now to FIG. 16, there is shown relative performance of theultracapacitor 10 in comparison to an otherwise equivalentultracapacitor. In FIG. 16A, leakage current is shown for a prior artembodiment of the ultracapacitor 10. In FIG. 16B, leakage current isshown for an equivalent ultracapacitor 10 that includes the barrier 30.In FIG. 16B, the ultracapacitor 10 is electrically equivalent to theultracapacitor whose leakage current is shown in FIG. 16A. In bothcases, the housing 7 was stainless steel, and the voltage supplied tothe cell was 1.75 Volts, and electrolyte was not purified. Temperaturewas held a constant 150 degrees Celsius. Notably, the leakage current inFIG. 16B indicates a comparably lower initial value and no substantialincrease over time while the leakage current in FIG. 16A indicates acomparably higher initial value as well as a substantial increase overtime.

Generally, the barrier 30 provides a suitable thickness of suitablematerials between the energy storage cell 12 and the housing 7. Thebarrier 30 may include a homogeneous mixture, a heterogeneous mixtureand/or at least one layer of materials. The barrier 30 may providecomplete coverage (i.e., provide coverage over the interior surface areaof the housing with the exception of electrode contacts) or partialcoverage. In some embodiments, the barrier 30 is formed of multiplecomponents. Consider, for example, the embodiment presented below andillustrated in FIG. 8.

Referring to FIG. 17, aspects of an additional embodiment are shown. Insome embodiments, the energy storage cell 12 is deposited within anenvelope 33. That is, the energy storage cell 12 has the barrier 30disposed thereon, wrapped thereover, or otherwise applied to separatethe energy storage cell 12 from the housing 7 once assembled. Theenvelope 33 may be applied well ahead of packaging the energy storagecell 12 into the housing 7. Therefore, use of an envelope 33 may presentcertain advantages, such as to manufacturers. (Note that the envelope 33is shown as loosely disposed over the energy storage cell 12 forpurposes of illustration).

In some embodiments, the envelope 33 is used in conjunction with thecoating, wherein the coating is disposed over at least a portion of theinterior surfaces. For example, in one embodiment, the coating isdisposed within the interior of the housing 7 only in areas where theenvelope 33 may be at least partially compromised (such as be aprotruding terminal 8). Together, the envelope 33 and the coating forman efficient barrier 30.

Accordingly, incorporation of the barrier 30 may provide for anultracapacitor that exhibits leakage current with comparatively lowinitial values and substantially slower increases in leakage currentover time in view of the prior art. Significantly, the leakage currentof the ultracapacitor remains at practical (i.e., desirably low) levelswhen the ultracapacitor is exposed to ambient temperatures for whichprior art capacitors would exhibit prohibitively large initial values ofleakage current and/or prohibitively rapid increases in leakage currentover time.

As a matter of convention, the term “leakage current” generally refersto current drawn by the capacitor which is measured after a given periodof time. This measurement is performed when the capacitor terminals areheld at a substantially fixed potential difference (terminal voltage).When assessing leakage current, a typical period of time is seventy two(72) hours, although different periods may be used. It is noted thatleakage current for prior art capacitors generally increases withincreasing volume and surface area of the energy storage media and theattendant increase in the inner surface area of the housing. In general,an increasing leakage current is considered to be indicative ofprogressively increasing reaction rates within the ultracapacitor 10.Performance requirements for leakage current are generally defined bythe environmental conditions prevalent in a particular application. Forexample, with regard to an ultracapacitor 10 having a volume of 20 mL, apractical limit on leakage current may fall below 100 mA.

Having thus described embodiments of the barrier 30, and various aspectsthereof, it should be recognized the ultracapacitor 10 may exhibit otherbenefits as a result of reduced reaction between the housing 7 and theenergy storage media 1. For example, an effective series resistance(ESR) of the ultracapacitor 10 may exhibit comparatively lower valuesover time. Further, unwanted chemical reactions that take place in aprior art capacitor often create unwanted effects such as out-gassing,or in the case of a hermetically sealed housing, bulging of the housing.In both cases, this leads to a compromise of the structural integrity ofthe housing and/or hermetic seal of the capacitor. Ultimately, this maylead to leaks or catastrophic failure of the prior art capacitor. Insome embodiments, these effects may be substantially reduced oreliminated by the application of a disclosed barrier 30.

It should be recognized that the terms “barrier” and “coating” are notlimiting of the teachings herein. That is, any technique for applyingthe appropriate material to the interior of the housing 7, body 20and/or cap 24 may be used. For example, in other embodiments, thebarrier 30 is actually fabricated into or onto material making up thehousing body 20, the material then being worked or shaped as appropriateto form the various components of the housing 7. When considering someof the many possible techniques for applying the barrier 30, it may beequally appropriate to roll on, sputter, sinter, laminate, print, orotherwise apply the material(s). In short, the barrier 30 may be appliedusing any technique deemed appropriate by a manufacturer, designerand/or user.

Materials used in the barrier 30 may be selected according to propertiessuch as reactivity, dielectric value, melting point, adhesion tomaterials of the housing 7, coefficient of friction, cost, and othersuch factors. Combinations of materials (such as layered, mixed, orotherwise combined) may be used to provide for desired properties.

Using an enhanced housing 7, such as one with the barrier 30, may, insome embodiments, limit degradation of the electrolyte 6. While thebarrier 30 presents one technique for providing an enhanced housing 7,other techniques may be used. For example, use of a housing 7 fabricatedfrom aluminum would be advantageous, due to the electrochemicalproperties of aluminum in the presence of electrolyte 6. However, giventhe difficulties in fabrication of aluminum, it has not been possible(until now) to construct embodiments of the housing 7 that takeadvantage of aluminum.

Additional embodiments of the housing 7 include those that presentaluminum to all interior surfaces, which may be exposed to electrolyte,while providing users with an ability to weld and hermetically seal thehousing. Improved performance of the ultracapacitor 10 may be realizedthrough reduced internal corrosion, elimination of problems associatedwith use of dissimilar metals in a conductive media and for otherreasons. Advantageously, the housing 7 makes use of existing technology,such available electrode inserts that include glass-to-metal seals (andmay include those fabricated from stainless steel, tantalum or otheradvantageous materials and components), and therefore is economic tofabricate.

Although disclosed herein as embodiments of the housing 7 that aresuited for the ultracapacitor 10, these embodiments (as is the case withthe barrier 30) may be used with any type of energy storage deemedappropriate, and may include any type of technology practicable. Forexample, other forms of energy storage may be used, includingelectrochemical batteries, in particular, lithium based batteries.

In some embodiments, a material used for construction of the body 20includes aluminum, which may include any type of aluminum or aluminumalloy deemed appropriate by a designer or fabricator (all of which arebroadly referred to herein simply as “aluminum”). Various alloys,laminates, and the like may be disposed over (e.g., clad to) thealuminum (the aluminum being exposed to an interior of the body 20).Additional materials (such as structural materials or electricallyinsulative materials, such as some polymer-based materials) may be usedto compliment the body and/or the housing 7. The materials disposed overthe aluminum may likewise be chosen by what is deemed appropriate by adesigner or fabricator.

In general, the material(s) exposed to an interior of the housing 7exhibit adequately low reactivity when exposed to the electrolyte 6, andtherefore are merely illustrative of some of the embodiments and are notlimiting of the teachings herein.

Although this example depicts only one feed-through 19 on the cap 24, itshould be recognized that the construction of the housing 7 is notlimited by the embodiments discussed herein. For example, the cap 24 mayinclude a plurality of feed-throughs 19. In some embodiments, the body20 includes a second, similar cap 24 at the opposing end of the annularcylinder. Further, it should be recognized that the housing 7 is notlimited to embodiments having an annular cylindrically shaped body 20.For example, the housing 7 may be a clamshell design, a prismaticdesign, a pouch, or of any other design that is appropriate for theneeds of the designer, manufacturer or user.

A highly efficient seal of the housing 7 is desired. That is, preventingintrusion of the external environment (such as air, humidity, etc, . . .) helps to maintain purity of the components of the energy storage cell12. Further, this prevents leakage of electrolyte 6 from the energystorage cell 12.

Referring now to FIG. 18, aspects of embodiments of a blank 34 for thecap 24 are shown. In FIG. 18A, the blank 34 includes a multi-layermaterial. A layer of a first material 41 is aluminum. A layer of asecond material 42 is stainless steel. In the embodiments of FIG. 18,the stainless steel is clad onto the aluminum, thus providing for amaterial that exhibits a desired combination of metallurgicalproperties. That is, in the embodiments provided herein, the aluminum isexposed to an interior of the energy storage cell (i.e., the housing),while the stainless steel is exposed to exterior. In this manner,advantageous electrical properties of the aluminum are enjoyed, whilestructural properties (and metallurgical properties, i.e., weldability)of the stainless steel are relied upon for construction. The multi-layermaterial may include additional layers as deemed appropriate.

As mentioned above, the layer of first material 41 is clad onto (orwith) the layer of second material 42. As used herein, the terms “clad,”“cladding” and the like refer to the bonding together of dissimilarmetals. Cladding is often achieved by extruding two metals through a dieas well as pressing or rolling sheets together under high pressure.Other processes, such as laser cladding, may be used. A result is asheet of material composed of multiple layers, where the multiple layersof material are bonded together such that the material may be workedwith as a single sheet (e.g., formed as a single sheet of homogeneousmaterial would be formed).

Referring still to FIG. 18A, in one embodiment, a sheet of flat stock(as shown) is used to provide the blank 34 to create a flat cap 24. Aportion of the layer of second material 42 may be removed (such asaround a circumference of the cap 24) in order to facilitate attachmentof the cap 24 to the body 20. In FIG. 18B, another embodiment of theblank 34 is shown. In this example, the blank 34 is provided as a sheetof clad material that is formed into a concave configuration. In FIG.18C, the blank 34 is provided as a sheet of clad material that is formedinto a convex configuration. The cap 24 that is fabricated from thevarious embodiments of the blank 34 (such as those shown in FIG. 18),are configured to support welding to the body 20 of the housing 7. Morespecifically, the embodiment of FIG. 18B is adapted for fitting withinan inner diameter of the body 20, while the embodiment of FIG. 18C isadapted for fitting over an outer diameter of the body 20. In variousalternative embodiments, the layers of clad material within the sheetmay be reversed.

When assembled, the cap 24 may be welded to the body 20, thus providingusers with a hermetic seal. Exemplary welding techniques include laserwelding and TIG welding, and may include other forms of welding asdeemed appropriate.

Referring now to FIG. 19, there is shown an embodiment of an electrodeassembly 50. The electrode assembly 50 is designed to be installed intothe blank 34 and to provide electrical communication from the energystorage media to a user. Generally, the electrode assembly 50 includes asleeve 51. The sleeve 51 surrounds the insulator 26, which in turnsurrounds the feed-through 19. In this example, the sleeve 51 is anannular cylinder with a flanged top portion.

In order to assemble the cap 24, a perforation (not shown) is made inthe blank 34. The perforation has a geometry that is sized to match theelectrode assembly 50. Accordingly, the electrode assembly 50 isinserted into perforation of the blank 34. Once the electrode assembly50 is inserted, the electrode assembly 50 may be affixed to the blank 34through a technique such as welding. The welding may be laser weldingwhich welds about a circumference of the flange of sleeve 51. Referringto FIG. 20, points 61 where welding is performed are shown. In thisembodiment, the points 61 provide suitable locations for welding ofstainless steel to stainless steel, a relatively simple weldingprocedure. Accordingly, the teachings herein provide for welding theelectrode assembly 50 securely into place on the blank 34.

Material for constructing the sleeve 51 may include various types ofmetals or metal alloys. Generally, materials for the sleeve 51 areselected according to, for example, structural integrity and bondability(to the blank 34). Exemplary materials for the sleeve 51 include 304stainless steel or 316 stainless steel. Material for constructing thefeed-through 19 may include various types of metals or metal alloys.Generally, materials for the feed-through 19 are selected according to,for example, structural integrity and electrical conductance. Exemplarymaterials for the electrode include 446 stainless steel or 52 alloy.

Generally, the insulator 26 is bonded to the sleeve 51 and thefeed-through 19 through known techniques (i.e., glass-to-metal bonding).Material for constructing the insulator 26 may include, withoutlimitation, various types of glass, including high temperature glass,ceramic glass or ceramic materials. Generally, materials for theinsulator are selected according to, for example, structural integrityand electrical resistance (i.e., electrical insulation properties).

Use of components (such as the foregoing embodiment of the electrodeassembly 50) that rely on glass-to-metal bonding as well as use ofvarious welding techniques provides for hermetic sealing of the energystorage. Other components may be used to provide hermetic sealing aswell. As used herein, the term “hermetic seal” generally refers to aseal that exhibits a leak rate no greater than that which is definedherein. However, it is considered that the actual seal efficacy mayperform better than this standard.

Additional or other techniques for coupling the electrode assembly 50 tothe blank 34 include use of a bonding agent under the flange of thesleeve 51 (between the flange and the layer of second material 42), whensuch techniques are considered appropriate.

Referring now to FIG. 21, the energy storage cell 12 is disposed withinthe body 20. The at least one terminal 8 is coupled appropriately (suchas to the feed-through 19), and the cap 24 is mated with the body 20 toprovide for the ultracapacitor 10.

Once assembled, the cap 24 and the body 20 may be sealed. FIG. 22depicts various embodiments of the assembled energy storage (in thiscase, the ultracapacitor 10). In FIG. 22A, a flat blank 34 (see FIG.18A) is used to create a flat cap 24. Once the cap 24 is set on the body20, the cap 24 and the body 20 are welded to create a seal 62. In thiscase, as the body 20 is an annular cylinder, the weld proceedscircumferentially about the body 20 and cap 24 to provide the seal 62.In a second embodiment, shown in FIG. 22B, the concave blank 34 (seeFIG. 18B) is used to create a concave cap 24. Once the cap 24 is set onthe body 20, the cap 24 and the body 20 are welded to create the seal62. In a third embodiment, shown in FIG. 22C, the convex blank 34 (seeFIG. 18C) is used to create a convex cap 24. Once the cap 24 is set onthe body 20, the cap 24 and the body 20 may be welded to create the seal62.

As appropriate, clad material may be removed (by techniques such as, forexample, machining or etching, etc, . . . ) to expose other metal in themulti-layer material. Accordingly, in some embodiments, the seal 62 mayinclude an aluminum-to-aluminum weld. The aluminum-to-aluminum weld maybe supplemented with other fasteners, as appropriate.

Other techniques may be used to seal the housing 7. For example, laserwelding, TIG welding, resistance welding, ultrasonic welding, and otherforms of mechanical sealing may be used. It should be noted, however,that in general, traditional forms of mechanical sealing alone are notadequate for providing the robust hermetic seal offered in theultracapacitor 10.

In some embodiments, the multi-layer material is used for internalcomponents. For example, aluminum may be clad with stainless steel toprovide for a multi-layer material in at least one of the terminals 8.In some of these embodiments, a portion of the aluminum may be removedto expose the stainless steel. The exposed stainless steel may then beused to attach the terminal 8 to the feed-through 19 by use of simplewelding procedures.

Using the clad material for internal components may call for particularembodiments of the clad material. For example, it may be beneficial touse clad material that include aluminum (bottom layer), stainless steeland/or tantalum (intermediate layer) and aluminum (top layer), whichthus limits exposure of stainless steel to the internal environment ofthe ultracapacitor 10. These embodiments may be augmented by, forexample, additional coating with polymeric materials, such as PTFE.

In general, assembly of the housing often involves placing the storagecell 12 within the body 20 and filling the body 20 with the electrolyte6. A drying process may be performed. Exemplary drying includes heatingthe body 20 with the storage cell 12 and electrolyte 6 therein, oftenunder a reduced pressure (e.g., a vacuum). Once adequate (optional)drying has been performed, final steps of assembly may be performed. Inthe final steps, internal electrical connections are made, the cap 24 isinstalled, and the cap 24 is hermetically sealed to the body 20, by, forexample, welding the cap 24 to the body 20.

Accordingly, providing a housing 7 that takes advantage of multi-layeredmaterial provides for an energy storage that exhibits leakage currentwith comparatively low initial values and substantially slower increasesin leakage current over time in view of the prior art. Significantly,the leakage current of the energy storage remains at practical (i.e.,desirably low) levels when the ultracapacitor 10 is exposed to ambienttemperatures for which prior art capacitors would exhibit prohibitivelylarge initial values of leakage current and/or prohibitively rapidincreases in leakage current over time.

Additionally, the ultracapacitor 10 may exhibit other benefits as aresult of reduced reaction between the housing 7 and the energy storagecell 12. For example, an effective series resistance (ESR) of the energystorage may exhibit comparatively lower values over time. Further, theunwanted chemical reactions that take place in a prior art capacitoroften create create unwanted effects such as out-gassing, or in the caseof a hermetically sealed housing, bulging of the housing 7. In bothcases, this leads to a compromise of the structural integrity of thehousing 7 and/or hermetic seal of the energy storage. Ultimately, thismay lead to leaks or catastrophic failure of the prior art capacitor.These effects may be substantially reduced or eliminated by theapplication of a disclosed barrier.

Accordingly, users are now provided with a housing 7 for the energystorage, where a substantial portion up to all of the interior surfacesof the housing 7 are aluminum (and may include a non-interferingmaterial, as described below). Thus, problems of internal corrosion areavoided and designers are afforded greater flexibility in selection ofappropriate materials for the electrolyte 6.

By use of a multi-layer material (e.g., a clad material), stainlesssteel may be incorporated into the housing 7, and thus components withglass-to-metal seals may be used. The components may be welded to thestainless steel side of the clad material using techniques such as laseror resistance welding, while the aluminum side of the clad material maybe welded to other aluminum parts (e.g., the body 20).

In some embodiments, an insulative polymer may be used to coat parts ofthe housing 7. In this manner, it is possible to insure that thecomponents of the energy storage are only exposed to acceptable types ofmetal (such as the aluminum). Exemplary insulative polymer includes PFA,FEP, TFE, and PTFE. Suitable polymers (or other materials) are limitedonly by the needs of a system designer or fabricator and the propertiesof the respective materials. Reference may be had to FIG. 23, where asmall amount of insulative material 39 is included to limit exposure ofelectrolyte 6 to the stainless steel of the sleeve 51 and thefeed-through 19. In this example, the terminal 8 is coupled to thefeed-through 19, such as by welding, and then coated with the insulativematerial 39.

Refer now to FIG. 24 in which aspects of assembly another embodiment ofthe cap 24 are depicted. FIG. 4A depicts a template (i.e., the blank 34)that is used to provide a body of the cap 24. The template is generallysized to mate with the housing 7 of an appropriate type of energystorage cell (such as the ultracapacitor 10). The cap 24 may be formedby initially providing the template forming the template, including adome 37 within the template (shown in FIG. 24B) and by then perforatingthe dome 37 to provide a through-way 32 (shown in FIG. 24C). Of course,the blank 34 (e.g., a circular piece of stock) may be pressed orotherwise fabricated such that the foregoing features are simultaneouslyprovided.

In general, and with regard to these embodiments, the cap may be formedof aluminum, or an alloy thereof. However, the cap may be formed of anymaterial that is deemed suitable by a manufacturer, user, designer andthe like. For example, the cap 24 may be fabricated from steel andpassivated (i.e., coated with an inert coating) or otherwise preparedfor use in the housing 7.

Referring now also to FIG. 25, there is shown another embodiment of theelectrode assembly 50. In these embodiments, the electrode assembly 50includes the feed-through 19 and a hemispherically shaped materialdisposed about the feed-through 19. The hemispherically shaped materialserves as the insulator 26, and is generally shaped to conform to thedome 37. The hemispheric insulator 26 may be fabricated of any suitablematerial for providing a hermetic seal while withstanding the chemicalinfluence of the electrolyte 6. Exemplary materials include PFA(perfluoroalkoxy polymer), FEP (fluorinated ethylene-propylene), PVF(polyvinylfluoride), TFE (tetrafluoroethylene), CTFE(chlorotrifluoroethylene), PCTFE (polychlorotrifluoroethylene), ETFE(polyethylenetetrafluoroethylene), ECTFE(polyethylenechlorotrifluoroethylene), PTFE (polytetrafluoroethylene),another fluoropolymer based material as well as any other material thatmay exhibit similar properties (in varying degrees) and provide forsatisfactory performance (such as by exhibiting, among other things, ahigh resistance to solvents, acids, and bases at high temperatures, lowcost and the like).

The feed-through 19 may be formed of aluminum, or an alloy thereof.However, the feed-through 19 may be formed of any material that isdeemed suitable by a manufacturer, user, designer and the like. Forexample, the feed-through 19 may be fabricated from steel and passivated(i.e., coated with an inert coating, such as silicon) or otherwiseprepared for use in the electrode assembly 50. An exemplary techniquefor passivation includes depositing a coating of hydrogenated amorphoussilicon on the surface of the substrate and functionalizing the coatedsubstrate by exposing the substrate to a binding reagent having at leastone unsaturated hydrocarbon group under pressure and elevatedtemperature for an effective length of time. The hydrogenated amorphoussilicon coating is deposited by exposing the substrate to siliconhydride gas under pressure and elevated temperature for an effectivelength of time.

The hemispheric insulator 26 may be sized relative to the dome 37 suchthat a snug fit (i.e., hermetic seal) is achieved when assembled intothe cap 24. The hemispheric insulator 26 need not be perfectly symmetricor of classic hemispheric proportions. That is, the hemisphericinsulator 26 is substantially hemispheric, and may include, for example,slight adjustments in proportions, a modest flange (such as at the base)and other features as deemed appropriate. The hemispheric insulator 26is generally formed of homogeneous material, however, this is not arequirement. For example, the hemispheric insulator 26 may include anair or gas filled torus (not shown) therein to provide for desiredexpansion or compressibility.

As shown in FIG. 26, the electrode assembly 50 may be inserted into thetemplate (i.e., the formed blank 34) to provide for an embodiment of thecap 24 that includes a hemispheric hermetic seal.

As shown in FIG. 27, in various embodiments, a retainer 43 may be bondedor otherwise mated to a bottom of the cap 24 (i.e., a portion of the cap24 that faces to an interior of the housing 7 and faces the energystorage cell 12). The retainer 43 may be bonded to the cap 24 throughvarious techniques, such as aluminum welding (such as laser, ultrasonicand the like). Other techniques may be used for the bonding, includingfor example, stamping (i.e., mechanical bonding) and brazing. Thebonding may occur, for example, along a perimeter of the retainer 43.Generally, the bonding is provided for in at least one bonding point tocreate a desired seal 71. At least one fastener, such as a plurality ofrivets may be used to seal the insulator 26 within the retainer 43.

In the example of FIG. 27, the cap 24 is of a concave design (see FIG.18B). However, other designs may be used. For example, a convex cap 24may be provided (FIG. 18C), and an over-cap 24 may also be used (avariation of the embodiment of FIG. 18C, which is configured to mount asdepicted in FIG. 22C).

In some embodiments, at least one of the housing 7 and the cap 24include materials that include a plurality of layers. For example, afirst layer of material may include aluminum, with a second layer ofmaterial being stainless steel. In this example, the stainless steel isclad onto the aluminum, thus providing for a material that exhibits adesired combination of metallurgical properties. That is, in theembodiments provided herein, the aluminum is exposed to an interior ofthe energy storage cell (i.e., the housing), while the stainless steelis exposed to exterior. In this manner, advantageous electricalproperties of the aluminum are enjoyed, while structural properties (andmetallurgical properties, i.e., weldability) of the stainless steel arerelied upon for construction. The multi-layer material may includeadditional layers as deemed appropriate. Advantageously, this providesfor welding of stainless steel to stainless steel, a relatively simplewelding procedure.

The material used for the cap as well as the feed-through 19 may beselected with regard for thermal expansion of the hemispheric insulator26. Further, manufacturing techniques may also be devised to account forthermal expansion. For example, when assembling the cap 24, amanufacturer may apply pressure to the hemispheric insulator 26, thus atleast somewhat compressing the hemispheric insulator 26. In this manner,there at least some thermal expansion of the cap 24 is provided forwithout jeopardizing efficacy of the hermetic seal.

While material used for construction of the body 20 includes aluminum,any type of aluminum or aluminum alloy deemed appropriate by a designeror fabricator (all of which are broadly referred to herein simply as“aluminum”). Various alloys, laminates, and the like may be disposedover (e.g., clad to) the aluminum (the aluminum being exposed to aninterior of the body 20. Additional materials (such as structuralmaterials or electrically insulative materials, such as somepolymer-based materials) may be used to compliment the body and/or thehousing 7. The materials disposed over the aluminum may likewise bechosen by what is deemed appropriate by a designer or fabricator.

Use of aluminum is not necessary or required. In short, materialselection may provide for use of any material deemed appropriate by adesigner, fabricator, or user and the like. Considerations may be givento various factors, such as, for example, reduction of electrochemicalinteraction with the electrolyte 6, structural properties, cost and thelike.

The storage cell 12 is now discussed in greater detail. Refer to FIG.28, where a cut-away view of the ultracapacitor 10 is provided. In thisexample, the storage cell 12 is inserted into and contained within thebody 20. Each plurality of leads are bundled together and coupled to thehousing 7 as one of the terminals 8. In some embodiments, the pluralityof leads are coupled to a bottom of the body 20 (on the interior), thusturning the body 20 into a negative contact 55. Likewise, anotherplurality of leads are bundled and coupled to the feed-through 19, toprovide a positive contact 56. Electrical isolation of the negativecontact 55 and the positive contact 56 is preserved by the electricalinsulator 26. Generally, coupling of the leads is accomplished throughwelding, such as at least one of laser and ultrasonic welding. Ofcourse, other techniques may be used as deemed appropriate.

It should be recognized that robust assembly techniques are required toprovide a highly efficient energy storage. Accordingly, some of thetechniques for assembly are now discussed.

Referring now to FIG. 29, components of an exemplary electrode 3 areshown. In this example, the electrode 3 will be used as the negativeelectrode 3 (however, this designation is arbitrary and merely forreferencing).

As may be noted from the illustration, at least in this embodiment, theseparator 5 is generally of a longer length and wider width than theenergy storage media 1 (and the current collector 2). By using a largerseparator 5, protection is provided against short circuiting of thenegative electrode 3 with the positive electrode 3. Use of additionalmaterial in the separator 5 also provides for better electricalprotection of the leads and the terminal 8.

Refer now to FIG. 30 which provides a side view of an embodiment of thestorage cell 12. In this example, a layered stack of energy storagemedia 1 includes a first separator 5 and a second separator 5, such thatthe electrodes 3 are electrically separated when the storage cell 12 isassembled into a rolled storage cell 23. Note that the term “positive”and “negative” with regard to the electrode 3 and assembly of theultracapacitor 10 is merely arbitrary, and makes reference tofunctionality when configured in the ultracapacitor 10 and charge isstored therein. This convention, which has been commonly adopted in theart, is not meant to apply that charge is stored prior to assembly, orconnote any other aspect other than to provide for physicalidentification of different electrodes.

Prior to winding the storage cell 12, the negative electrode 3 and thepositive electrode 3 are aligned with respect to each other. Alignmentof the electrodes 3 gives better performance of the ultracapacitor 10 asa path length for ionic transport is generally minimized when there is ahighest degree of alignment. Further, by providing a high degree ofalignment, excess separator 5 is not included and efficiency of theultracapacitor 10 does not suffer as a result.

Referring now also to FIG. 31, there is shown an embodiment of thestorage cell 12 wherein the electrodes 3 have been rolled into therolled storage cell 23. One of the separators 5 is present as anoutermost layer of the storage cell 12 and separates energy storagemedia 1 from an interior of the housing 7.

“Polarity matching” may be employed to match a polarity of the outermostelectrode in the rolled storage cell 23 with a polarity of the body 20.For example, in some embodiments, the negative electrode 3 is on theoutermost side of the tightly packed package that provides the rolledstorage cell 23. In these embodiments, another degree of assuranceagainst short circuiting is provided. That is, where the negativeelectrode 3 is coupled to the body 20, the negative electrode 3 is theplaced as the outermost electrode in the rolled storage cell 23.Accordingly, should the separator 5 fail, such as by mechanical wearinduced by vibration of the ultracapacitor 10 during usage, theultracapacitor 10 will not fail as a result of a short circuit betweenthe the outermost electrode in the rolled storage cell 23 and the body20.

For each embodiment of the rolled storage cell 23, a reference mark 72may be in at least the separator 5. The reference mark 72 will be usedto provide for locating the leads on each of the electrodes 3. In someembodiments, locating of the leads is provided for by calculation. Forexample, by taking into account an inner diameter of the jelly roll andan overall thickness for the combined separators 5 and electrodes 3, alocation for placement of each of the leads may be estimated. However,practice has shown that it is more efficient and effective to use areference mark 72. The reference mark 72 may include, for example, aslit in an edge of the separator(s) 5.

Generally, the reference mark 72 is employed for each new specificationof the storage cell 12. That is, as a new specification of the storagecell 12 may call for differing thickness of at least one layer therein(over a prior embodiment), use of prior reference marks may be at leastsomewhat inaccurate.

In general, the reference mark 72 is manifested as a single radial linethat traverses the roll from a center thereof to a periphery thereof.Accordingly, when the leads are installed along the reference mark 72,each lead will align with the remaining leads (as shown in FIG. 10).However, when the storage cell 12 is unrolled (for embodiments where thestorage cell 12 is or will become a roll), the reference mark 72 may beconsidered to be a plurality of markings (as shown in FIG. 32). As amatter of convention, regardless of the embodiment or appearance ofmarking of the storage cell 12, identification of a location forincorporation of the lead is considered to involve determination of a“reference mark 72” or a “set of reference marks 72.”

Referring now to FIG. 32, once the reference mark 72 has beenestablished (such as by marking a rolled up storage cell 12), aninstallation site for installation each of the leads is provided (i.e.,described by the reference mark 72). Once each installation site hasbeen identified, for any given build specification of the storage cell12, the relative location of each installation site may be repeated foradditional instances of the particular build of storage cell 12.

Generally, each lead is coupled to a respective current collector 2 inthe storage cell 12. In some embodiments, both the current collector 2and the lead are fabricated from aluminum. Generally, the lead iscoupled to the current collector 2 across the width, W, however, thelead may be coupled for only a portion of the width, W. The coupling maybe accomplished by, for example, ultrasonic welding of the lead to thecurrent collector 2. In order to accomplish the coupling, at least someof the energy storage media 1 may be removed (as appropriate) such thateach lead may be appropriately joined with the current collector 2.Other preparations and accommodations may be made, as deemedappropriate, to provide for the coupling.

Of course, opposing reference marks 73 may be included. That is, in thesame manner as the reference marks 72 are provided, a set of opposingreference marks 73 may be made to account for installation of leads forthe opposing polarity. That is, the reference marks 72 may be used forinstalling leads to a first electrode 3, such as the negative electrode3, while the opposing reference marks 73 may be used for installingleads to the positive electrode 3. In the embodiment where the rolledstorage cell 23 is cylindrical, the opposing reference marks 73 aredisposed on an opposite side of the energy storage media 1, and offsetlengthwise from the reference marks 72 (as depicted).

Note that in FIG. 32, the reference marks 72 and the opposing referencemarks 73 are both shown as being disposed on a single electrode 3. Thatis, FIG. 29 depicts an embodiment that is merely for illustration ofspatial (i.e., linear) relation of the reference marks 72 and theopposing reference marks 73. This is not meant to imply that thepositive electrode 3 and the negative electrode 3 share energy storagemedia 1. However, it should be noted that in instances where thereference marks 72 and the opposing reference marks 73 are placed byrolling up the storage cell 12 and then marking the separator 5, thatthe reference marks 72 and the opposing reference marks 73 may indeed byprovided on a single separator 5. However, in practice, only one set ofthe reference marks 72 and the opposing reference marks 73 would be usedto install the leads for any given electrode 3. That is, it should berecognized that the embodiment depicted in FIG. 32 is to be complimentedwith another layer of energy storage media 1 for another electrode 3which will be of an opposing polarity.

As shown in FIG. 33, the foregoing assembly technique results in astorage cell 12 that includes at least one set of aligned leads. A firstset of aligned leads 91 are particularly useful when coupling the rolledstorage cell 23 to one of the negative contact 55 and the positivecontact 56, while a set of opposing aligned leads 92 provide forcoupling the energy storage media 1 to an opposite contact (55, 56).

The rolled storage cell 23 may be surrounded by a wrapper 93. Thewrapper 93 may be realized in a variety of embodiments. For example, thewrapper 93 may be provided as KAPTON™ tape (which is a polyimide filmdeveloped by DuPont of Wilmington Del.), or PTFE tape. In this example,the KAPTON™ tape surrounds and is adhered to the rolled storage cell 23.The wrapper 93 may be provided without adhesive, such as a tightlyfitting wrapper 93 that is slid onto the rolled storage cell 23. Thewrapper 93 may be manifested more as a bag, such as one that generallyengulfs the rolled storage cell 23 (e.g., such as the envelope 73discussed above). In some of these embodiments, the wrapper 93 mayinclude a material that functions as a shrink-wrap would, and therebyprovides an efficient physical (and in some embodiments, chemical)enclosure of the rolled storage cell 23. Generally, the wrapper 93 isformed of a material that does not interfere with electrochemicalfunctions of the ultracapacitor 10. The wrapper 93 may also providepartial coverage as needed, for example, to aid insertion of the rolledstorage cell 23.

In some embodiments, the negative leads and the positive leads arelocated on opposite sides of the rolled storage cell 23 (in the case ofa jelly-roll type rolled storage cell 23, the leads for the negativepolarity and the leads for the positive polarity may be diametricallyopposed). Generally, placing the leads for the negative polarity and theleads for the positive polarity on opposite sides of the rolled storagecell 23 is performed to facilitate construction of the rolled storagecell 23 as well as to provide improved electrical separation.

In some embodiments, once the aligned leads 91, 92 are assembled, eachof the plurality of aligned leads 91, 92 are bundled together (in place)such that a shrink-wrap (not shown) may be disposed around the pluralityof aligned leads 91, 92. Generally, the shrink-wrap is formed of PTFE,however, any compatible material may be used.

In some embodiments, once shrink-wrap material has been placed about thealigned leads 91, the aligned leads 91 are folded into a shape to beassumed when the ultracapacitor 10 has been assembled. That is, withreference to FIG. 34, it may be seen that the aligned leads assume a “Z”shape. After imparting a “Z-fold” into the aligned leads 91, 92 andapplying the shrink-wrap, the shrink-wrap may be heated or otherwiseactivated such that the shrink-wrap shrinks into place about the alignedleads 91, 92. Accordingly, in some embodiments, the aligned leads 91, 92may be strengthened and protected by a wrapper. Use of the Z-fold isparticularly useful when coupling the energy storage media 1 to thefeed-through 19 disposed within the cap 24.

Of course, other embodiments for coupling each set of aligned leads 91,92 (i.e., each terminal 8) to a respective contact 55, 56 may bepracticed. For example, in one embodiment, an intermediate lead iscoupled to the one of the feed-through 19 and the housing 7, such thatcoupling with a respectice set of aligned leads 91, 92 is facilitated.

Materials used may be selected according to properties such asreactivity, dielectric value, melting point, adhesion to othermaterials, weldability, coefficient of friction, cost, and other suchfactors. Combinations of materials (such as layered, mixed, or otherwisecombined) may be used to provide for desired properties.

In a variety of embodiments, it is useful to use a plurality of theultracapacitors 10 together to provide a power supply. In order toprovide for reliable operation, individual ultracapacitors 10 may betested in advance of use. In order to perform various types of testing,each of the ultracapacitors 10 may be tested as a singular cell, inseries or in parallel with multiple ultracapacitors 10 attached. Usingdifferent metals joined by various techniques (such as by welding) canreduce the ESR of the connection as well as increase the strength of theconnections. Some aspects of connections between ultracapacitors 10 arenow introduced.

In some embodiments, the ultracapacitor 10 includes two contacts. Thetwo contacts are the glass-to-metal seal pin (i.e., the feed-through 19)and the entire rest of the housing 7. When connecting a plurality of theultracapacitors 10 in series, it is often desired to couple aninterconnection between a bottom of the housing 7 (in the case of thecylindrical form housing 7), such that distance to the internal leads isminimized, and therefore of a minimal resistance. In these embodiments,an opposing end of the interconnection is usually coupled to the pin ofthe glass-to-metal seal.

With regard to interconnections, a common type of weld involves use of aparallel tip electric resistance welder. The weld may be made byaligning an end of the interconnection above the pin and welding theinterconnection directly to the pin. Using a number of welds willincrease the strength and connection between the interconnection and thepin. Generally, when welding to the pin, configuring a shape of the endof the interconnection to mate well with the pin serves to ensure thereis substantially no excess material overlapping the pin that would causea short circuit.

An opposed tip electric resistance welder may be used to weld theinterconnection to the pin, while an ultrasonic welder may used to weldthe interconnection to the bottom of the housing 7. Soldering techniquesmay used when metals involved are compatible.

With regard to materials used in interconnections, a common type ofmaterial used for the interconnection is nickel. Nickel may be used asit welds well with stainless steel and has a strong interface. Othermetals and alloys may be used in place of nickel, for example, to reduceresistance in the interconnection.

Generally, material selected for the interconnection is chosen forcompatibility with materials in the pin as well as materials in thehousing 7. Exemplary materials include copper, nickel, tantalum,aluminum, and nickel copper clad. Further metals that may be usedinclude silver, gold, brass, platinum, and tin.

In some embodiments, such as where the pin (i.e., the feed-through 19)is made of tantalum, the interconnection may make use of intermediatemetals, such as by employing a short bridge connection. An exemplarybridge connection includes a strip of tantalum, which has been modifiedby use of the opposed tip resistance welder to weld a strip ofaluminum/copper/nickel to the bridge. A parallel resistance welder isthen used to weld the tantalum strip to the tantalum pin.

The bridge may also be used on the contact that is the housing 7. Forexample, a piece of nickel may be resistance welded to the bottom of thehousing 7. A strip of copper may then be ultrasonic welded to the nickelbridge. This technique helps to decrease resistance of cellinterconnections. Using different metals for each connection can reducethe ESR of the interconnections between cells in series.

Having thus described aspects of a robust ultracapacitor 10 that isuseful for high temperature environments (i.e., up to about 210 degreesCelsius), some additional aspects are now provided and/or defined.

A variety of materials may be used in construction of the ultracapacitor10. Integrity of the ultracapacitor 10 is essential if oxygen andmoisture are to be excluded and the electrolyte 6 is to be preventedfrom escaping. To accomplish this, seam welds and any other sealingpoints should meet standards for hermiticity over the intendedtemperature range for operation. Also, materials selected should becompatible with other materials, such as ionic liquids and solvents thatmay be used in the formulation of the electrolyte 6.

In some embodiments, the feed-through 19 is formed of metal such as atleast one of KOVAR™ (a trademark of Carpenter Technology Corporation ofReading, Pa., where KOVAR is a vacuum melted, iron-nickel-cobalt, lowexpansion alloy whose chemical composition is controlled within narrowlimits to assure precise uniform thermal expansion properties), Alloy 52(a nickel iron alloy suitable for glass and ceramic sealing to metal),tantalum, molybdenum, niobium, tungsten, Stainless Steel 446 (aferritic, non-heat treatable stainless steel that offers good resistanceto high temperature corrosion and oxidation) and titanium.

The body of glass-to-metal seals that take advantage of the foregoingmay be fabricated from 300 series stainless steels, such as 304, 304L,316, and 316L alloys. The bodies may also be made from metal such as atleast one of various nickel alloys, such as Inconel (a family ofaustenitic nickel-chromium-based superalloys that are oxidation andcorrosion resistant materials well suited for service in extremeenvironments subjected to pressure and heat) and Hastelloy (a highlycorrosion resistant metal alloy that includes nickel and varyingpercentages of molybdenum, chromium, cobalt, iron, copper, manganese,titanium, zirconium, aluminum, carbon, and tungsten).

The insulating material between the feed-through 19 and the surroundingbody in the glass-to-metal seal is typically a glass, the composition ofwhich is proprietary to each manufacturer of seals and depends onwhether the seal is under compression or is matched. Other insulativematerials may be used in the glass-to-metal seal. For example, variouspolymers may be used in the seal. As such, the term “glass-to-metal”seal is merely descriptive of a type of seal, and is not meant to implythat the seal must include glass.

The housing 7 for the ultracapacitor 10 may be made from, for example,types 304, 304L, 316, and 316L stainless steels. They may also beconstructed from, but not limited to, some of the aluminum alloys, suchas 1100, 3003,5052, 4043 and 6061. Various multi-layer materials may beused, and may include, for example, aluminum clad to stainless steel.Other non-limiting compatible metals that may be used include platinum,gold, rhodium, ruthenium and silver.

Specific examples of glass-to-metal seals that have been used in theultracapacitor 10 include two different types of glass-to-metal seals. Afirst one is from SCHOTT with a US location in Elmsford, N.Y. Thisembodiment uses a stainless steel pin, glass insulator, and a stainlesssteel body. A second glass-to-metal seal is from HERMETIC SEALTECHNOLOGY of Cincinnatti, Ohio. This second embodiment uses a tantalumpin, glass insulator and a stainless steel body. Varying sizes of thevarious embodiments may be provided.

An additional embodiment of the glass-to-metal seal includes anembodiment that uses an aluminum seal and an aluminum body. Yet anotherembodiment of the glass-to-metal seal includes an aluminum seal usingepoxy or other insulating materials (such as ceramics or silicon).

A number of aspects of the glass-to-metal seal may be configured asdesired. For example, dimensions of housing and pin, and the material ofthe pin and housing may be modified as appropriate. The pin can also bea tube or solid pin, as well as have multiple pins in one cover. Whilethe most common types of material used for the pin are stainless steelalloys, copper cored stainless steel, molybdenum, platinum-iridium,various nickel-iron alloys, tantalum and other metals, somenon-traditional materials may be used (such as aluminum). The housing isusually formed of stainless steel, titanium and/or various othermaterials.

A variety of fastening techniques may be used in assembly of theultracapacitor 10. For example, and with regards to welding, a varietyof welding techniques may be used. The following is an illustrativelisting of types of welding and various purposes for which each type ofwelding may be used.

Ultrasonic welding may be used for, among other things: welding aluminumtabs to the current collector; welding tabs to the bottom clad cover;welding a jumper tab to the clad bridge connected to the glass-to-metalseal pin; and welding jelly roll tabs together. Pulse or resistancewelding may be used for, among other things: welding leads onto thebottom of the can or to the pin; welding leads to the current collector;welding a jumper to a clad bridge; welding a clad bridge to the terminal8; welding leads to a bottom cover. Laser welding may be used for, amongother things: welding a stainless steel cover to a stainless steel can;welding a stainless steel bridge to a stainless steel glass-to-metalseal pin; and welding a plug into the fill port. TIG welding may be usedfor, among other things: sealing aluminum covers to an aluminum can; andwelding aluminum seal into place. Cold welding (compressing metalstogether with high force) may be used for, among other things: sealingthe fillport by force fitting an aluminum ball/tack into the fill port.

Physical aspects of an exemplary ultracapacitor 10 are now provided.Note that in the following tables, the terminology “tab” generallyrefers to the “lead” as discussed above; the terms “bridge” and “jumper”also making reference to aspects of the lead (for example, the bridgemay be coupled to the feed-through, or “pin,” while the jumper is usefulfor connecting the bridge to the tabs, or leads). Use of variousconnections may facilitate the assembly process, and take advantage ofcertain assembly techniques. For example, the bridge may be laser weldedor resistance welded to the pin, and coupled with an ultrasonic weld tothe jumper.

TABLE 7 Weights of Complete Cell With Electrolyte Weight PercentComponent (grams) of total SS Can (body of the housing) 14.451 20.87% SSTop cover (cap) 5.085 7.34% Tantalum glass-metal Seal 12.523 18.09%SS/Al Clad Bottom 10.150 14.66% Tack (seal for fill hole) 0.200 0.29%Inner Electrode (cleared, no tabs) 3.727 5.38% Inner Electrode Aluminum1.713 2.47% Inner Electrode Carbon 2.014 2.91% Outer Electrode (cleared,no tabs) 4.034 5.83% Outer Electrode Aluminum 1.810 2.61% OuterElectrode Carbon 2.224 3.21% Separator 1.487 2.15% Alum. Jelly roll Tabs(all 8) 0.407 0.59% Ta/Al clad bridge 0.216 0.31% Alum. Jumper(bridge-JR tabs) 0.055 0.08% Teflon heat shrink 0.201 0.29% Electrolyte(IT) 16.700 24.12% Total Weight 69.236 100.00%

TABLE 8 Weights of Complete Cell Without Electrolyte Weight PercentComponent (grams) of total SS Can 14.451 27.51% SS Top cover 5.085 9.68%Tantalum glass-metal Seal 12.523 23.84% SS/Al Clad Bottom 10.150 19.32%Tack 0.200 0.38% Inner Electrode (cleared, no 3.727 7.09% tabs) OuterElectrode (cleared, no 4.034 7.68% tabs) Separator 1.487 2.83% Alum.Jelly roll Tabs (all 8) 0.407 0.77% Ta/Al clad bridge 0.216 0.41% Alum.Jumper (bridge-JR tabs) 0.055 0.10% Teflon heat shrink 0.201 0.38% TotalWeight 52.536 100.00%

TABLE 9 Weights of Cell Components in Full Cell with Electrolyte WeightPercent Component (grams) of total Can, covers, seal, bridge, 42.88161.93% jumper, heat shrink, tack Jelly Roll with Electrodes, 9.65513.95% tabs, separator Electrolyte 16.700 24.12% Total Weight 69.236100.00%

TABLE 10 Weights of Electrode Weight Percent of Component (grams) totalInner electrode carbon 2.014 25.95% Inner electrode aluminum 1.71322.07% Outer electrode carbon 2.224 28.66% Outer electrode aluminum1.810 23.32% Total Weight 7.761 100.00%

As a demonstration of purity in the ultracapacitor 10, the housing 7 ofa sealed ultracapacitor 10 was opened, and the storage cell 12 wassampled for impurities. Water content was measured using the KarlFischer method for the electrodes, separator and electrolyte from thecell 12. Three measurements were taken and averaged.

The water content (i.e., a level of moisture) of electrode and separatorwas found to be 343.3 ppm (per weight percent) and 152.6 ppm (per weightpercent) respectively. In order to measure water content in electrolyte6, 1.1 ml of electrolyte which had been obtained from the closed cellwas mixed with 4 ml of purified electrolyte. The water content of themixture was then measured. By knowing the water content in the addedelectrolyte (60.3 ppm), the water content of the electrolyte withdrawnfrom the cell was determined. Thus, the water content of the electrolyte6 within the sealed ultracapacitor 10 was 15.5 ppm. Halide content inthe ultracapacitor 10 was measured using Ion Selective Electrodes (ISE).The average chloride (Cl—) ion content was found to be 90.9 ppm in theelectrolyte 6, while the average fluoride (F—) content was found to be0.25 ppm.

In general, a method for characterizing a contaminant within theultracapacitor includes breaching the housing 7 to access contentsthereof, sampling the contents and analyzing the sample. Techniquesdisclosed elsewhere herein may be used in support of the characterizing.

Note that to ensure accurate measurement of impurities in theultracapacitor and components thereof, including the electrode, theelectrolyte and the separator, assembly and disassembly may be performedin an appropriate environment, such as in an inert environment within aglove box.

FIGS. 35-38 are graphs depicting performance of exemplaryultracapacitors 10. FIGS. 35 and 36 depict performance of theultracapacitor 10 at 1.75 volts and 125 degrees Celsius. FIGS. 37 and 38depict performance of the ultracapacitor 10 at 1.5 volts and 150 degreesCelsius.

Generally, the ultracapacitor 10 may be used under a variety ofenvironmental conditions and demands. For example, terminal voltage mayrange from about 100 mV to 10 V. Ambient temperatures may range fromabout minus 40 degrees Celsius to plus 210 degrees Celsius. Typical hightemperature ambient temperatures range from plus 60 degrees Celsius toplus 210 degrees Celsius.

FIGS. 39-43 are additional graphs depicting performance of exemplaryultracapacitors 10. In these examples, the ultracapacitor 10 was aclosed cell (i.e., housing). The ultracapacitor was cycled 10 times,with a charge and discharge of 100 mA, charged to 0.5 Volts, resistancemeasurement, discharged to 10 mV, 10 second rest then cycled again.

Tables 11 and 12 provide comparative performance data for embodiments ofthe ultracapacitor 10. The performance data was collected for a varietyof operating conditions as shown.

TABLE 11 Comparative Performance Data ESR Capacitance Cell EndingTemperature Voltage Time Initial % ESR Initial % Capacitance WeightCurrent Cell # (° C.) (V) (Hrs) (mOhm) Increase (F) Decrease (g) (mA)D2011-09 150 1.25 1500 30 0 93  5 — 0.5 C1041-02 150 1.5 1150 45 60 32 —28.35 0.5 C2021-01 150 1.5 1465 33 100 32 70 26.61 0.8 D5311-01 150 1.6150 9 10 87  4 — 5 C6221-05 150 1.75 340 15 50 — — 38.31 1 C6221-05 1501.75 500 15 100 — — 38.31 2 C6221-05 150 1.75 600 15 200 — — 38.31 2C6221-05 150 1.75 650 15 300 — — 38.31 2 D1043-02 150 1.75 615 43 50 100— — 3 D1043-02 150 1.75 700 43 100 100 — — 3 C5071-01 150 1.75 600 26100 27 32 — 2 C5071-01 150 1.75 690 26 200 27 35 — 2 C5071-01 150 1.75725 26 300 27 50 — 2 C8091-06 125 1.75 500 38 5 63 11 37.9  0.5 C9021-02125 1.75 1250 37 10 61 — 39.19 0.3 D5011-02 125 1.9 150 13 0 105  0 —1.4 C8091-06 125 2 745 41 22 56 37.9  1.2 D2011-08 175 1 650 33 12 89 30— 4 D1043-10 175 1.3 480 30 100 93 50 — 6.5 C2021-04 175 1.4 150 35 10027 — 27.17 3.5 C4041-04 210 0.5 10 28 0 32 — 28.68 1 C4041-04 210 0.5 2028 0 32 — 28.68 7 C4041-04 210 0.5 50 28 100 32 — 28.68 18

TABLE 12 Comparative Performance Data Volumetric ESR Initial LeakageVolumetric Volumetric Leakage T Voltage Time Initial Capacitance CurrentESR Capacitance Current % ESR % Capacitance Volume Cell # (° C.) (V)(Hrs) (mOhm) (F) (mA) (Ohms × cc) (F/cc) (mA/cc) Increase Decrease (cc)D2011-09 150 1.25 1500 30 93 0.5 0.75 3.72 0.02 0 5 25 C2021-01 150 1.51465 33 32 0.75 0.396 2.67 0.06 100 5 12 C5071-01 150 1.75 600 26 27 20.338 2.08 0.15 100 32 13 C5071-01 150 1.75 690 26 27 2 0.338 2.08 0.15200 35 13 C5071-01 150 1.75 725 26 27 2 0.338 2.08 0.15 300 50 13C8091-06 125 1.75 500 38 63 0.5 0.494 4.85 0.04 5 11 13 C9021-02 1251.75 1250 37 61 0.25 0.481 4.69 0.02 10 11 13 D2011-08 175 1 650 33 89 40.825 3.56 0.16 12 30 25 D1043-10 175 1.3 480 30 93 6.5 0.75 3.72 0.26100 50 25 C4041-04 210 0.5 50 28 32 18 0.336 2.67 1.50 100 50 12

Thus, data provided in Tables 11 and 12 demonstrate that the teachingsherein enable performance of ultracapitors in extreme conditions.Ultracapacitors fabricated accordingly may, for example, exhibit leakagecurrents of less than about 1 mA per milliliter of cell volume, and anESR increase of less than about 100 percent in 500 hours (while held atvoltages of less than about 2 V and temperatures less than about 150degrees Celsius). As trade-offs may be made among various demands of theultracapacitor (for example, voltage and temperature) performanceratings for the ultracapacitor may be managed (for example, a rate ofincrease for ESR, capacitance,) may be adjusted to accommodate aparticular need. Note that in reference to the foregoing, “performanceratings” is given a generally conventional definition, which is withregard to values for parameters describing conditions of operation.

Note that measures of capacitance as well as ESR, as presented in Table11 and elsewhere herein, followed generally known methods. Considerfirst, techniques for measuring capacitance.

Capacitance may be measured in a number of ways. One method involvesmonitoring the voltage presented at the capacitor terminals while aknown current is drawn from (during a “discharge”) or supplied to(during a “charge”) of the ultracapacitor. More specifically, we may usethe fact that an ideal capacitor is governed by the equation:I=C*dV/dt,where I represents charging current, C represents capacitance and dV/dtrepresents the time-derivative of the ideal capacitor voltage, V. Anideal capacitor is one whose internal resistance is zero and whosecapacitance is voltage-independent, among other things. When thecharging current, I, is constant, the voltage V is linear with time, sodV/dt may be computed as the slope of that line, or as DeltaV/DeltaT.However, this method is generally an approximation and the voltagedifference provided by the effective series resistance (the ESR drop) ofthe capacitor should be considered in the computation or measurement ofa capacitance. The effective series resistance (ESR) may generally be alumped element approximation of dissipative or other effects within acapacitor. Capacitor behavior is often derived from a circuit modelcomprising an ideal capacitor in series with a resistor having aresistance value equal to the ESR. Generally, this yields goodapproximations to actual capacitor behavior.

In one method of measuring capacitance, one may largely neglect theeffect of the ESR drop in the case that the internal resistance issubstantially voltage-independent, and the charging or dischargingcurrent is substantially fixed. In that case, the ESR drop may beapproximated as a constant and is naturally subtracted out of thecomputation of the change in voltage during said constant-current chargeor discharge. Then, the change in voltage is substantially a reflectionof the change in stored charge on the capacitor. Thus, that change involtage may be taken as an indicator, through computation, of thecapacitance.

For example, during a constant-current discharge, the constant current,I, is known. Measuring the voltage change during the discharge, DeltaV,during a measured time interval DeltaT, and dividing the current value Iby the ratio DeltaV/DeltaT, yields an approximation of the capacitance.When I is measured in amperes, DeltaV in volts, and DeltaT in seconds,the capacitance result will be in units of Farads.

Turning to estimation of ESR, the effective series resistance (ESR) ofthe ultracapacitor may also be measured in a number of ways. One methodinvolves monitoring the voltage presented at the capacitor terminalswhile a known current is drawn from (during a “discharge”) or suppliedto (during a “charge”) the ultracapacitor. More specifically, one mayuse the fact that ESR is governed by the equation:V=I*R,where I represents the current effectively passing through the ESR, Rrepresents the resistance value of the ESR, and V represents the voltagedifference provided by the ESR (the ESR drop). ESR may generally be alumped element approximation of dissipative or other effects within theultracapacitor. Behavior of the ultracapacitor is often derived from acircuit model comprising an ideal capacitor in series with a resistorhaving a resistance value equal to the ESR. Generally, this yields goodapproximations of actual capacitor behavior.

In one method of measuring ESR, one may begin drawing a dischargecurrent from a capacitor that had been at rest (one that had not beencharging or discharging with a substantial current). During a timeinterval in which the change in voltage presented by the capacitor dueto the change′ in stored charge on the capacitor is small compared tothe measured change in voltage, that measured change in voltage issubstantially a reflection of the ESR of the capacitor. Under theseconditions, the immediate voltage change presented by the capacitor maybe taken as an indicator, through computation, of the ESR.

For example, upon initiating a discharge current draw from a capacitor,one may be presented with an immediate voltage change DeltaV over ameasurement interval DeltaT. So long as the capacitance of thecapacitor, C, discharged by the known current, I, during the measurementinterval, DeltaT, would yield a voltage change that is small compared tothe measured voltage change, DeltaV, one may divide DeltaV during thetime interval DeltaT by the discharge current, I, to yield anapproximation to the ESR. When I is measured in amperes and DeltaV involts, the ESR result will have units of Ohms.

Both ESR and capacitance may depend on ambient temperature. Therefore, arelevant measurement may require the user to subject the ultracapacitor10 to a specific ambient temperature of interest during the measurement.

Performance requirements for leakage current are generally defined bythe environmental conditions prevalent in a particular application. Forexample, with regard to a capacitor having a volume of 20 mL, apractical limit on leakage current may fall below 100 mA. As referred toherein, a “volumetric leakage current” of the ultracapacitor 10generally refers to leakage current divided by a volume of theultracapacitor 10, and may be expressed, for example in units of mA/cc.Similarly, a “volumetric capacitance” of the ultracapacitor 10 generallyrefers to capacitance of the ultracapacitor 10 divided by the volume ofthe ultracapacitor 10, and may be expressed, for example in units ofF/cc. Additionally, “volumetric ESR” of the ultracapacitor 10 generallyrefers to ESR of the ultracapacitor 10 multiplied by the volume of theultracapacitor 10, and may be expressed, for example in units ofOhms·cc.

Note that one approach to reduce the volumetric leakage current at aspecific temperature is to reduce the operating voltage at thattemperature. Another approach to reduce the volumetric leakage currentat a specific temperature is to increase the void volume of theultracapacitor. Yet another approach to reduce the leakage current is toreduce loading of the energy storage media 1 on the electrode 3.

A variety of environments may exist where the ultracapacitor 10 is ofparticular usefulness. For example, in automotive applications, ambienttemperatures of 105 degrees Celsius may be realized (where a practicallifetime of the capacitor will range from about 1 year to 20 years). Insome downhole applications, such as for geothermal well drilling,ambient temperatures of 300 degrees Celsius or more may be reached(where a practical lifetime of the capacitor will range from about 100hours to 10,000 hours).

A “lifetime” for the capacitor is also generally defined by a particularapplication and is typically indicated by a certain percentage increasein leakage current or degradation of another parameter (as appropriateor determinative for the given application). For instance, in oneembodiment, the lifetime of a capacitor in an automotive application maybe defined as the time at which the leakage current increases to 200% ofits initial (beginning of life or “BOL”) value.

Electrolyte 6 may be selected for exhibiting desirable properties, suchas high thermal stability, a low glass transition temperature (Tg), aviscosity, a particular rhoepectic or thixotropic property (e.g., onethat is dependent upon temperature), as well as high conductivity andexhibited good electric performance over a wide range of temperatures.As examples, the electrolyte 6 may have a high degree of fluidicity, or,in contrast, be substantially solid, such that separation of electrodes3 is assured. Accordingly, other embodiments of electrolyte 6 thatexhibit the desired properties may be used as well or in conjunctionwith any of the foregoing.

“Peak power density” is one fourth times the square of peak devicevoltage divided by the effective series resistance of the device.“Energy density” is one half times the square of the peak device voltagetimes the device capacitance.

For the purposes of this invention, an ultracapacitor 10 may have avolume in the range from about 0.05 cc to about 7.5 liters.

Nominal values of normalized parameters may be obtained by multiplyingor dividing the normalized parameters (e.g. volumetric leakage current)by a normalizing characteristic (e.g. volume). For instance, the nominalleakage current of an ultracapacitor having a volumetric leakage currentof 10 mA/cc and a volume of 50 cc is the product of the volumetricleakage current and the volume, 500 mA. Meanwhile the nominal ESR of anultracapacitor having a volumetric ESR of 20 mOhm·cc and a volume of 50cc is the quotient of the volumetric ESR and the volume, 0.4 mOhm.

A volume of a particular ultracapacitor 10 may be extended by combiningseveral storage cells (e.g., welding together several jelly rolls)within one housing 7 such that they are electrically in parallel or inseries.

Embodiments of the ultracapacitor 10 that exhibit a relatively smallvolume may be fabricated in a prismatic form factor such that theelectrodes 3 of the ultracapacitor 10 oppose one another, at least oneelectrode 3 having an internal contact to a glass to metal seal, theother having an internal contact to a housing or to a glass to metalseal.

It should be recognized that the teachings herein are merelyillustrative and are not limiting of the invention. Further, one skilledin the art will recognize that additional components, configurations,arrangements and the like may be realized while remaining within thescope of this invention. For example, configurations of layers,electrodes, leads, terminals, contacts, feed-throughs, caps and the likemay be varied from embodiments disclosed herein. Generally, designand/or application of components of the ultracapacitor andultracapacitors making use of the electrodes are limited only by theneeds of a system designer, manufacturer, operator and/or user anddemands presented in any particular situation.

Further, various other components may be included and called upon forproviding for aspects of the teachings herein. For example, additionalmaterials, combinations of materials and/or omission of materials may beused to provide for added embodiments that are within the scope of theteachings herein. As discussed herein, terms such as “adapting,”“configuring,” “constructing” and the like may be considered to involveapplication of any of the techniques disclosed herein, as well as otheranalogous techniques (as may be presently known or later devised) toprovide an intended result.

When introducing elements of the present invention or the embodiment(s)thereof, the articles “a,” “an,” and “the” are intended to mean thatthere are one or more of the elements. Similarly, the adjective“another,” when used to introduce an element, is intended to mean one ormore elements. The terms “including,” “has” and “having” are intended tobe inclusive such that there may be additional elements other than thelisted elements.

In the present application a variety of variables are described,including but not limited to components (e.g. electrode materials,electrolytes, etc.), conditions (e.g., temperature, freedom from variousimpurities at various levels), and performance characteristics (e.g.,post-cycling capacity as compared with initial capacity, low leakagecurrent, etc.). It is to be understood that any combination of any ofthese variables can define an embodiment of the invention. For example,a combination of a particular electrode material, with a particularelectrolyte, under a particular temperature range and with impurity lessthan a particular amount, operating with post-cycling capacity andleakage current of particular values, where those variables are includedas possibilities but the specific combination might not be expresslystated, is an embodiment of the invention. Other combinations ofarticles, components, conditions, and/or methods can also bespecifically selected from among variables listed herein to define otherembodiments, as would be apparent to those of ordinary skill in the art.

It will be recognized that the various components or technologies mayprovide certain necessary or beneficial functionality or features.Accordingly, these functions and features as may be needed in support ofthe appended claims and variations thereof, are recognized as beinginherently included as a part of the teachings herein and a part of theinvention disclosed.

While the invention has been described with reference to exemplaryembodiments, it will be understood that various changes may be made andequivalents may be substituted for elements thereof without departingfrom the scope of the invention. In addition, many modifications will beappreciated to adapt a particular instrument, situation or material tothe teachings of the invention without departing from the essentialscope thereof. Therefore, it is intended that the invention not belimited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention but to be construed by theclaims appended herein.

What is claimed is:
 1. An ultracapacitor comprising: a positiveelectrode, a negative electrode, a separator, and an electrolyte withina hermetically sealed housing, wherein the ultracapacitor has less than200 ppm of halides and a water content of less than 100 ppm, wherein theultracapacitor exhibits an equivalent series resistance (ESR) increaseof less than about 300 percent while held at a constant voltage for atleast 20 hours while held at a substantially constant temperature withina temperature range of between about 80 degrees Celsius and 210 degreesCelsius, and wherein: the ultracapacitor is configured to operate at atemperature between 80 degrees Celsius and 210 degrees Celsius with avolumetric leakage current of less than 1,000 mAmp per Liter, and/or theultracapacitor exhibits a volumetric leakage current of less than 10mA/cc while held at a substantially constant temperature between 100degrees Celsius and 150 degrees Celsius.
 2. The ultracapacitor of claim1, wherein the ESR increase is less than about 100 percent.
 3. Theultracapacitor of claim 1, wherein at least one of the positiveelectrode and the negative electrode comprises a carbonaceous energystorage media comprising at least one of activated carbon, carbonfibers, rayon, graphene, aerogel, carbon cloth, and carbon nanotubes. 4.The ultracapacitor of claim 1, wherein the electrolyte comprises anionic liquid comprising: a cation selected from the group consisting ofammonium cations, imidazolium cations, functionalized imidazoliumcations, oxazolium cations, phosphonium cations, piperidinium cations,pyrazinium cations, pyrazolium cations, pyridazinium cations, pyridiniumcations, pyrimidinium cations, pyrrolidinium cations, sulfonium cations,thiazolium cations, triazolium cations, guanidium cations,isoquinolinium cations, benzotriazolium cations, and viologen-typecations; and an anion selected from the group consisting ofbis(trifluoromethanesulfonate)imide,tris(trifluoromethanesulfonate)methide, dicyanamide, tetra-fluoroborate,hexafluorophosphate, trifluoromethanesulfonate,bis(pentafluoroethanesulfonate)-imide, thiocyanate, andtrifluoro(trifluoromethyl)borate.
 5. The ultracapacitor of claim 4,wherein the electrolyte further comprises a solvent selected from thegroup consisting of acetonitrile, amides, benzonitrile, butyrolactone,cyclic ether, diethylether, dimethoxyethane, dimethylformamide,dimethylsulfone, dioxane, dioxolane, ethyl formate, ethylene carbonate,ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, propylenecarbonate, dibutyl carbonate, lactone, methyl formate, methylpropionate, methyltetrahydrofuran, tetrahydrofuran, nitrobenzene,nitromethane, N-methylpyrrolidone, sulfolane, tetramethylene sulfone,thiophene, ethyleneglycol, diethylene glycol, triethylene glycol,polyethylene glycols, carbonic acid ester, γ-butyrolactone, andtricyanohexane.
 6. The ultracapacitor of claim 1, wherein thehermetically sealed housing exhibits a leakage rate of helium that isbetween about 10⁻⁵ standard He cc/second and about 10⁻⁹ standard Hecc/second.
 7. The ultracapacitor of claim 1, wherein the hermeticallysealed housing exhibits a leakage rate of helium that is between about10⁻⁷ standard He cc/second and about 10⁻¹⁰ standard He cc/second.
 8. Theultracapacitor of claim 1, wherein the temperature range is betweenabout 100 degrees Celsius and about 210 degrees Celsius.
 9. Theultracapacitor of claim 1, wherein the temperature range is betweenabout 150 degrees Celsius and about 210 degrees Celsius.